Skip to main content

Full text of "Journal of the Society of Motion Picture Engineers"

See other formats


From the collection of the 



n 



Prelinger 
v JJibrary 



t 



San Francisco, California 
2007 



)LUME XXVII NUMBER ONE 

JOURNAL 

of the 

SOCIETY OF MOTION 
PICTURE ENGINEERS 






JULY, 1936 



LISHED MONTHLY BY THE SOCIETY OF MOTION PICTURE ENGINEER 



FALL CONVENTION 

Society of Motion Picture Engineers 

Sagamore Hotel 

Rochester, N. Y. 

October I2th to I5th, Inclusive 



Technical Sessions 

On the Roof of the Sagamore Hotel and at the plants of the Eastman Kodak Co. 
and the Bausch & Lomb Optical Co. Symposiums, General Discussions, Lectures, 
Demonstrations, Open Forums. 

Semi* Annual Banquet 

Wednesday evening at Oak Hill Country Club Dining, dancing, music, enter- 
tainment, addresses by eminent members of the industry. 

Hotel Rates 

Minimum rates and excellent accommodations guaranteed to members: Single, 
$3.50 per day; double, $6.00 per day; parlor suites, double, $10; parlor suites, 
triple, $12.00 per day. Make reservations as early as possible to assure satisfactory 
accommodations. 

Program 

See page 120, this issue of the JOURNAL. 



Papers for the Fall Convention 

Manuscripts of papers received before August 20th will be given 
immediate consideration by the Papers Committee and the Board of 
Editors. The best of these manuscripts will be selected and given 
preferred positions upon the program of the Convention, with ample 
time for presentation and discussion, or about thirty minutes to one 
hour. The remaining manuscripts will be considered for the pro- 
gram, but with limited time for presentation. 

The remainder of the program will be filled as manuscripts are 
received, until September 20th, after which date no papers will be 
accepted unless the subject matter contained therein is particularly 
outstanding or timely. Titles and abstracts of all papers will be 
published in the October issue if received by September 1st. 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXVII JULY, 1936 Number 1 



CONTENTS 

Page 

Progress in the Motion Picture Industry Report of the Prog- 
ress Committee 3 

A Study of Theater Loud Speakers and the Resultant Develop- 
ment of the Shearer Two- Way Horn System . . J. K. HILLIARD 45 

Dividing Networks for Loud Speaker Systems 

J. K. HILLIARD AND H. R. KIMBALL 61 

Television, from the Standpoint of the Motion Picture Produc- 
tion Industry Report of the Scientific Committee of the 
Research Council of the Academy of Motion Picture Arts 

and Sciences 74 

Activities of Science Service in Scientific Documentation 

WATSON DAVIS 77 
Some Technical Aspects of Microphotography . . R. H. DRAEGER 84 

Microfilm Copying of Documents T. R. SCHELLENBERG 90 

New Motion Picture Apparatus 

New Background Projector for Process Cinematography .... 

H. GRIFFIN 96 

RCA Photophone High-Fidelity Sound Reproducing Equip- 
ment J. FRANK, JR. 99 

Optical Reduction Sound Printer M. E. COLLINS 105 

Thyratron Reactor Theater Lighting Control 

J. R. MANHEIMER 107 
Foto Fade, a Chemical and Dye Mixture for Positive Fades 

T. R. BARRABEE 112 

Committees of the Society 113 

Fall, 1936, Convention at Rochester, N. Y., October 12-15, 

Inclusive 118 

Society Announcements 122 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors 

J. I. CRABTREE, Chairman 

O. M. GLUNT A. C. HARDY L. A. JONES 

G. E. MATTHEWS 



Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscriptions or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 

Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1936, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is 
not responsible for statements made by authors. 



Officers of the Society 

President: HOMER G. TASKER, Universal City, Calif. 

Past-President: ALFRED N. GOLDSMITH, 444 Madison Ave., New York, N. Y. 
Executive Vice-President: SIDNEY K. WOLF, 250 W. 57th St., New York, N. Y. 
Engineering Vice-President: LOYD A. JONES, Kodak Park, Rochester, N. Y. 
Editorial Vice-President: JOHN I. CRABTREE, Kodak Park, Rochester, N. Y. 
Financial Vice-President: OMER M. GLUNT, 463 West St., New York, N. Y. 
Convention Vice-President: WILLIAM C. KUNZMANN, Box 6087, Cleveland, Ohio. 
Secretary: JOHN H. KURLANDER, 2 Clearfield Ave., Bloomfield, N. J. 
Treasurer: TIMOTHY E. SHEA, 463 West St., New York, N. Y. 

Governors 

MAX C. BATSEL, Front & Market Sts., Camden, N. J. 

LAWRENCE W. DAVEE, 250 W. 57th St., New York, N. Y. 

ARTHUR S. DICKINSON, 28 W. 44th St., New York, N. Y. 

HERBERT GRIFFIN, 90 Gold St., New York, N. Y. 

ARTHUR C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

EMERY HUSE, 6706 Santa Monica Blvd., Hollywood, Calif. 

GERALD F. RACKETT, 823 N. Seward St., Hollywood, Calif. 

CARRINGTON H. STONE, 205 W. Wacker Drive, Chicago, 111. 



See p. 113 for Technical Committees 



PROGRESS IN THE MOTION PICTURE INDUSTRY 
REPORT OF THE PROGRESS COMMITTEE* 

Summary. This report of the Progress Committee covers the year 1935. The 
advances in the cinematographic art are classified as follows : (I) Cinematography; 
(II) Sound Recording; (III) Sound and Picture Reproduction; (IV) Film Labora- 
tory Practice and Sensitometry ; (V) Publications and New Books; Appendix A 
General Field of Progress of the Motion Picture Industry in Great Britain; Ap- 
pendix B General Field of Progress of the Motion Picture Industry in Japan. 

INTRODUCTION 

The Committee believes itself very fortunate this year in being 
able to collect a great deal of material representing new advances in 
equipment and in the art of cinematography. It is to be expected, 
of course, that a great many items* that should find their way into a 
report of this nature will be missing; this can not be attributed to 
any dereliction on the part of the Committee members, but rather 
to the inability of the interested parties to supply the Committee 
with information to be included in the report. 

As is noted in the body of the report, color photography made 
great strides during the year with the introduction of Kodachrome 
in the amateur field and the extensive use of Technicolor in feature 
productions. 

The advent of the long-awaited silent camera seemed to come nearer 
in 1935, and descriptions of new silent and nearly silent cameras are 
contained in- the following report of the Committee. 

Another item of interest partially developed during the year is 
the new high-pressure air-cooled and water-cooled mercury arcs which 
threatened to revolutionize the art of stage and screen lighting, and 
incidentally offered a new tool for recording sound. It is to be 
expected that considerable progress will be made by the various 
branches of cinematography in adopting these arcs during 1936. 

In the field of sound recording, considerable progress is to be noted 
during the year just closed. Push-pull recording gained a strong foot- 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 



4 PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. p. E. 

hold in Hollywood and promises to play an important part in studio 
production work during the coming year. Invalidation of the Tri- 
Ergon patents has led to the development of new sound reproducing 
systems utilizing principles previously barred by the claims of the 
now defunct patents. 

Advancement in sound reproduction was made during the year with 
the introduction of the new multicellular, or Fletcher, type of horn, 
which was used so successfully in the binaural transmission of 
orchestral music between Philadelphia and Washington. 

The Committee is glad to include in the report items from Germany 
and an excellent report of progress in Japan and Great Britain, in 
which latter country considerable progress has been evident during 
the past year. The Committee wishes to thank the following firms 
for supplying materials and photographs for the report: Bell & 
Howell Company; Electrical Research Products, Inc.; General 
Radio Company; Mitchell Camera Corporation; RCA Manufactur- 
ing Co.; Mole-Richardson, Inc.; Technicolor Motion Picture 
Corporation; Twentieth Century-Fox Films, Inc.; Fearless Camera 
Company; Klangfilm, G. m. b. H*. 

J. G. FRAYNE, Chairman 

L. N. BUSCH R. E. FARNHAM H. MEYER 

A. A. COOK E. R. GEIB V. E. MILLER 

R. M. CORBIN A. M. GUNDELFINGER S. S. A. WATKINS 

J. A. DUBRAY G. E. MATTHEWS I. D. WRATTEN 



Subject Classification 

(I) CINEMATOGRAPHY 

(.4) Professional 

(1) Films and Emulsions 

(2) Cameras and Accessories 

(3) Lenses and Shutters 

(4) Stage Illumination 

(5) Color 

(B) Amateur 

(1) Films 

(2) Cameras 

(3) Projectors 

(4) 16-Mm. Sound Printer 

(5) Projectors 

(6) Color 

(7) Miscellaneous Equipment 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 5 

(II) SOUND RECORDING 

(1) General 

(2) Recording Equipment 

(3) Re-Recording and Playback Equipment 

(4) Testing and Miscellaneous 

(III) SOUND AND PICTURE REPRODUCTION 

(1) Sound Equipment 

(2) Projectors and Accessories 

(IV) LABORATORY PRACTICE AND SENSITOMETRY 

(V) PUBLICATIONS AND NEW BOOKS 
APPENDIX A 

General Field of Progress in the Motion Picture Industry in Great 
Britain. 

APPENDIXB 

General Field of Progress in the Motion Picture Industry in Japan. 

(I) CINEMATOGRAPHY 

(^4) Professional 

(1) Film and Emulsions. The introduction of Kodachrome film 
in April, 1935, marked one of the greatest achievements of the 
emulsion manufacturer and research chemist. Although available 
only in 16-mm. width, the significance of the emulsion makers' skill 
is nevertheless supreme, because this product requires no less than 
five separate coatings besides the anti-halo coatings upon the back. 
During reversal development, the silver image in each emulsion is 
transformed into a dye image complementary in color to the color 
to which the emulsion was sensitive. The high sensitivity of the emul- 
sions, necessitating only a slight increase of exposure over that re- 
quired for ordinary photography, is another useful property of this 
new color process. 1 

Besides this noteworthy contribution in the field of color, further 
improvement in negative emulsions was evidenced by the introduc- 
tion of emulsions of still greater speed than had been available before 
1935. These new materials of satisfactory color-sensitivity and low 
graininess quickly found application both in the studio and for news 
photography under poor lighting conditions. 2 

Of theoretical interest were the studies made of the effect of using 



6 



PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. P. E. 



ultrasonic vibrations in connection with the preparation of emulsions. 
Claus described an improved method of optical sensitizing which 
consisted in dyeing the silver bromide (free of carrier) and then dis- 
persing it in the gelatin by ultrasonic waves. 3 It was found by Dan- 
gers that the quality of emulsions peptized by ultrasonic waves 




FIG. 1. Silent camera (Twentieth Century- Fox Film Corp.) 



depended upon the nature of the surface of the silver halide grains 
upon the addition of the gelatin solution. 4 

A further paper on emulsion technic was published by Fuchs, 
which described the control of grain size by crystallization inhibitors, 
the use of dialdehydes to control physical hardening, and the addition 
of fog-clearing amines. 5 

Summaries were given of the progress made in Russia in photo- 
graphic research and in the manufacture of photographic materials. 
While the volume of production had greatly improved, the quality of 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 7 

the film support and the emulsions was not as satisfactory as had been 
expected. 6 Subjects discussed by Russian investigators included, 
among others : (1) the influence of acid substrata upon photographic 
properties; (2) the effect of pH upon hypersensitization with am- 




FIG. 2. Technicolor three-color camera (Technicolor Mo- 
tion Picture Corp.), 

monia and various buffer solutions ; ( 3) the influence of replacements 
of groupings in thiocyanine dyes upon their usefulness as optical 
sensitizers. 

Loss of sensitivity resulting from bathing various types of photo- 
graphic emulsions in water before exposure for different times was 



8 PROGRESS IN MOTION PICTURE INDUSTRY (J. S. M. p. E. 

reported by Charriou and Valette, who found that the loss of red 
sensitivity was half that of blue for a panchromatic material. 7 

The chemistry of the cyanine dye series was dealt with extensively 




FIG. 3. New studio camera (Mitchell Camera Co.). 

by Brooker and his co-workers in a group of six papers. 8 A paper 
was published also by Brooker and Keyes upon new sensitizers for 
the infrared, which described the preparation of tetra- and penta- 
carbo-cy anines . 9 

(2) Cameras and Accessories. Perhaps this year's most interest- 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 9 

ing announcement 10 in professional camera design was made by the 
technical staff of the Twentieth Century-Fox Film Corporation 
(Fig. 1). The general layout of the camera developed by this com- 
pany adheres essentially to conventional American practice; that is, 
a four-lens turret is used, a durable metal box houses the camera 
mechanism itself and is surmounted by a dual external film magazine 
of 1000-ft. capacity, while the driving motor is mounted at the rear. 
Access to the mechanism is through a door on the left-hand side, 




FIG. 4. Panoram dolly (Fearless Camera Co.). 

at which side is mounted also a finder interlocked with the focusing 
mechanism. 

The camera housing is cylindrical, which shape is best suited to 
the rotating focusing shift employed. The rotation brings the focus- 
ing microscope into place between the lens and a fixed eyepiece at 
the rear. A conventional, but carefully balanced disk type of shutter 
is used, having an aperture of 200 degrees. 

The film-propelling mechanism employs registering pilot pins, and 
the motion of the driving pins and their characteristic of straight-line 
engagement and disengagement and uniform acceleration have per- 
mitted reducing the period of take-down while still maintaining de- 
sirable uniformity of motion. 

Silence is achieved by this uniformity of action of the movement, 
by reducing the amount of gearing and the weight of the moving 



10 PROGRESS IN MOTION PICTURE INDUSTRY [j. S. M. p. E. 

parts, and by giving to the film as free a path as possible. Magazine 
noise is minimized by affording the film free passage, and by elimi- 
nating contact between the edges of the film and the walls of the 
magazine. Provision has been made for using a variety of standard 
driving motors. The mounting of the finder is of the conventional 
form, interlocking with the lens-focusing mechanism to correct for 
focus and parallax. Parallax compensation is provided by a lateral 
movement of the finder lens which may be roughly compared to the 
sliding front board of a still camera. 

A new camera for the three-color Techniclor process 11 has a double 
film-gate at right angles. At one aperture a super sensitive film for 
the green negative is photographed; at the other, a bi-pack photo- 
graphic record is taken, the red-sensitive negative being back of a 
blue-sensitive film (Fig. 2). 

The optical system consists of a specially designed photographic 
objective and a beam-splitting prism. The filtering action for color- 
selectivity is provided by suitable green and magenta filters. With 
regard to outside appearance, the camera is designed upon conven- 
tional lines. Provisions have been made for perfect registration of 
the images and for critical focusing. 

The new Mitchell studio camera was designed to meet the needs 
of the present sound stages for a silent, light-weight, compact, and 
convenient camera (Fig. 3). The most significant changes are the 
addition of an automatic dissolve, and the replacement of the four- 
lens turret by a single lens with bayonet lock. Outside the camera 
proper the finder has been arranged to focus and parallax automati- 
cally in conjunction with changing the lens focus in follow or follow- 
focus shots. All this mechanism, together with the magazine and 
motor, and with the exception of the finder and follow-focus mecha- 
nism, is in an insulated housing, the function of which is to absorb 
the sound. 

The operating controls are all on the outside, so that it is necessary 
to open the outer housing only to thread the camera. All other 
operations, such as focusing, changing the magnification on the focus 
tube, changing the filters in the focus tube, the hand dissolve and 
the automatic dissolve, are all accomplished from the outside. The 
weight of the whole equipment with 1000 feet of film is 135 pounds, 
which is considerably lighter than the lightest blimp in use. The 
camera is adapted to use either the Western Electric interlock motors 
or the regular synchronous motors. 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 



11 




FIG. 5. Elimination of reflections from store window by Eastman 
Pola-Screen: (upper) without screen; (lower) with screen. 

The Fox-Fearless type of dolly, or velocilator, has found its way 
into nearly all the larger studios because of its mobility and the ease 
with which it handles the heavier blimps. A new type of velocilator, 
made by both Fearless and Raby, carrying the boom arm upon a 
turntable, is fast becoming popular (Fig. 4) . The great improvements 



12 PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. p. E. 

that have been made in such devices will no doubt make them an 
accepted part of every camera equipment, replacing tripods except 
for special shots, even when cameras return to their pre-sound weights. 

(3) Lenses and Shutters. No exceptional advancements have 
been made in camera lenses during 1935. A faster series of Speed 
Panchro lenses (//1. 3, 2V4-inch focus) has been put upon the market. 
Altman has described in the JOURNAL 12 a revolving panoramic lens 
that has unusual possibilities as a wide-angle lens. A more detailed 
description of the German mirror telephoto lenses has been pub- 
lished, 13 and there are the usual patents on new or improved forms 
of lenses. 14 

A very interesting accessory to the optical field is the Pola-Screen 
introduced by the Eastman Kodak Company. This screen gives the 
operator a hitherto impossible control of the polarized light entering 
the lens of the camera, making available several of its peculiar 
characteristics. The elimination of reflections is now simple, maxi- 
mum results being attained when the optical axis of the lens is at a 
32-degree angle from the reflecting surface, as at that angle the light 
reflected from most surfaces is fully polarized (Fig. 5). Sky-filtering 
is possible when the lens axis is at right angles to the sun's rays, 
which will prove of value in color photography, since the Pola-Screen 
is of neutral color value. 

The Pola-Screen opens up possibilities also in the field of stereo- 
scopy, applying it in a manner somewhat similar to viewing a blue and 
red positive through corresponding blue and red glasses, but without 
the color interference. A description of the possibilities of the filters 
has been published by Tuttle and McFarlane, 15 and DeVinna has 
written an account of practical experience with these filters in cine- 
matography. 16 

(4) Stage Illumination. The rapid progress made in new types 
of gaseous conductor lamps during the past year or so continues to 
be of outstanding interest in the lighting industry as a whole. The 
laboratories of the Philips Lamp Company of Holland, as well as 
those of the General Electric Company in the United States, have 
produced mercury vapor lamps of the air-cooled type having bright- 
nesses of the order of 20,000 candles per square-inch ; and of the water- 
cooled type, about 150,000 candles per square-inch. By way of com- 
parison, the old familiar Cooper-Hewitt mercury vapor tube had a 
brightness of 15 candles per square-inch, and the high-efficiency in- 
candescent lamp can be operated at brightnesses up to 20,000 candles 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 



13 



per square-inch. These lamps, in general, consists of a quartz tube 
with electrodes at each end, and are enclosed within a protective 
housing. The experimental air-cooled lamps had light-sources 
approximately 4 millimeters in diameter and about 10 millimeters 
in length. The water-cooled types were slightly smaller. Since they 
possess the characteristics of an arc, 
they must be used in conjunction 
with either a resistor or reactance 
ballast. 

Operating the mercury vapor source 
at these high brightnesses results in 
considerable improvement in the 
quality of the light, but nevertheless 
the light retains much of its usual 
blue-green properties. At the present 
time their application as light-sources 
for studio motion picture photog- 
raphy appears rather remote, par- 
ticularly when the severe require- 
ments of color photography are con- 
sidered. The extremely great bright- 
ness of the water-cooled lamp offers 
possibilities as a projection source. 

Since photography is so dependent 
upon the source of light, mention 
should be made of the new Mole- 
Richardson spotlights for both incan- 
descent and arc lighting. Their 2000- 
watt Junior and 5000-watt Senior 
Solar Spots, with Fresnel lenses, pro- 
vide a uniform field of illumination 
with no "ghost." This likewise ap- 
plies to their so-called HI type of high-intensity arc spot, which is 
especially valuable in color photography and is finding a place in 
black-and-white photography also because of the reasons mentioned 
above. Their 120-ampere spot (Fig. 6) has an intensity equivalent 
to that of the 24-inch Sun arc; and their 150-ampere spot is claimed 
to equal the 36-inch Sun arc in intensity. In both lamps the beam 
may be varied from parallel to a 44-degree angle. 

(5) Color. The revived interest in color processes noted in 




FIG. 6. 120-ampere spotlight 
with Fresnel lens (Mole-Richard- 
son, Inc.). 



14 PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. p. E. 

1934 continued throughout 1935, stimulated no doubt by the intro- 
duction of the Kodachrome process mentioned earlier in this report. 
At a symposium on color photography held at the Hollywood Con- 
vention in May, Ball described the technical aspects of the Techni- 
color process. The first three-color, feature-length motion picture 
was released in June. It was entitled Becky Sharp, and was made by 
the Technicolor imbibition process. The picture was made entirely 




FIG. 7. Double-eight|inodel 134A camera (8-mm.) 
(Bell & Howell Co.). 

by artificial light; but a second feature, The Trail of the Lonesome 
Pine, released in the Spring of 1936, was made almost exclusively 
outdoors. 

Technicolor made great advances with their three-color process, 
with pictures now showing or in production that will no doubt revive 
color interest in the industry. Good definition, depth of focus, and 
a conservation of color values make the process the only practical one 
to date in the 35-mm. field. 

A comprehensive paper was published by Caspar giving a critical 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 15 

commentary on additive and subtractive processes of photography 
and details of the entire production and processing of Gasparcolor 
film. The incorporation of actual dyes (polyazo), instead of esters 
of vat leuco dyes formerly employed, is claimed to offer the advantage 
of advance determination of both shade and concentration of the dye. 
Sensitization of the new material is not complementary, i. e., the 
yellow layer is green sensitive; the magenta layer, red sensitive; 
and the blue-green layer, sensitive to the infrared. 17 

Emulsions available for amateur color cinematography included, 
besides Kodachrome, a screen-coated emulsion known as Dufaycolor 
and a fine-lined lenticular film called Ultra-Chrome Color Film. 18 A 
detailed description of the method of preparing the Dufaycolor screens 
and processing the film was given by Renwick, who states that copies 
may be produced both by projection and by contact printing. 19 The 
characteristics and applications of the lenticular screen were treated 
by Heymer. 20 The same author gives a comprehensive review of 
color-films by the "Silver-Dye Bleaching" process. 20 

(J5) Amateur 

1935 has been an eventful year in the substandard cine field. It 
has brought about interesting developments in equipment and 
processes, and has again demonstrated the tendency of the manu- 
facturer to improve and refine existing equipment. Public interest 
in amateur cinematography has been stimulated by the introduction 
of new developments in 8-mm. equipment, and by the improvement 
in sound equipment and color in the 16-mm. field. 

The development of 16-mm. projectors with increased light and 
adequate sound, capable of serving large audiences, and the general 
use of fine-grained films are gradually raising the 16-mm. film from 
strictly amateur use to that of semi-professional. Similar develop- 
ments in fine-grained film and improvement in equipment have re- 
sulted in a general acceptance of 8-mm. film for amateur use. 

(1) Films. Filmopan, an extremely fine-grained reversible 8-mm. 
film was produced by Agfa Ansco Corporation for the Filmo straight- 
eight camera. The film is 8 millimeters wide, and carries perforations 
on one side in the conventional manner. 

(2) Cameras. Bell & Howell have entered the 8-mm. field and 
introduced a straight-eight and a double-eight camera (Fig. 7). 
Both are designed according to entirely new principles, and offer 



16 PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. p. E. 

the utmost in simplicity of operation. The Filmo straight-eight 
accommodates 30 feet of straight 8-mm. film, whereas the double- 
eight takes film of 16-mm. width which is divided into 8-mm. strips 
after being processed. In the straight-eight there are no sprockets 
to be laced. Spools are held in the hand, and the film end is quickly 
engaged through the hub of the take-up spool ; both spools are then 
dropped upon the spindles of the camera without having to check 
loops, sprockets, or aperture gate. The gate is automatically held 
open, and closes when the camera door is shut, automatically engag- 
ing the shuttle tooth. 

The camera incorporates a built-in view-finder with auxiliary 
masks attached so as to be instantly positioned according to the focal 
length of the lens used. It is equipped with the 21.5-mm. //2.5 
Taylor, Taylor, Hobson lens, and has four film speeds: 8, 16, 24, and 
32 frames per second. A special model is also available with speeds 
ranging from 16 to 64 frames per second. An exposure dial is built 
into the camera door. Auxiliary lenses are available in focal lengths 
of 1 and 1.5 inches, and vary in speed from //1. 5 to //3.5. An in- 
genious lens mount is provided which enables the lenses to be changed 
instantly. 

A magazine Cine Kodak using 16-mm. film has been placed upon 
the market. It operates at speeds of 8, 16, and 64 frames per second, 
and has interchangeable telephoto lenses ranging from 1-inch //1. 9 
to 6-inch //4. 5. The eye-level view-finder incorporated in the carry- 
ing handle is adjustable to serve all five lenses. A new type of maga- 
zine is employed carrying 50 feet of film, either Cine* Kodak panchro- 
matic, Cine Kodak 6*5 panchromatic, or Kodachrome. Each maga- 
zine carries its own footage meter and normally is closed. When the 
magazine is placed into the camera and the camera closed, the film 
aperture of the magazine is opened. The act of opening the camera 
after exposure closes the aperture on the magazine. No frames are 
therefore lost. 

(3) Projectors. The Ampro Corporation announced a new design 
in the barrel type of shutter used in their projectors, resulting in 
a screen brilliancy 90 per cent greater, with the same 750-watt 
source, than was heretofore possible. 

A new model 40 Kodascope 8 was made available to replace the 
model 25. This projector utilizes a 200-watt lamp, making possible 
large screen images and greater brilliancy from 8-mm. film. 

A new, heavy-duty, 16-mm. projector for auditorium use has been 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 



announced by DeVry. The outstanding feature of this projector is 
the incorporation of an intermittent sprocket instead of the more 
familiar claw to effect the step-motion of the film. 

(4) 16-Mm. Sound Printer. The RCA Manufacturing Company, 
Inc., developed and furnished to a 

number of film laboratories process- 
ing 16-mm. sound-film an optical 
reduction printer for making 16-mm. 
sound-track prints from 35-mm. 
sound negatives. 

These printers were developed in 
order to make available to the 
users of 16-mm. equipment sound 
prints having an extended frequency 
range and free from flutter or 
sprocket modulation. The printers 
do not scan the sound-track to be 
printed; but, instead, a section of 
the 35-mm. film is imaged upon the 
16-mm. stock. This system elimi- 
nates the effect of the width of the 
light-beam on the 16-mm. film, 
which in systems in which the scan- 
ning is done through narrow slits so 
that the 16-mm. film is exposed by 
a thin modulated light-beam, results 
in distortion and losses at the higher 
frequencies. 

The printer is shown in Fig. 8. 
It is driven by a three-phase syn- 
chronous motor. The 35-mm. film 
runs at 90 feet per minute. To insure smooth film motion, a 
mechanical filter system of the rotary stabilizer type is used. 

(5) Sound Projectors. The Bell & Howell Company introduced 
a 1000-watt sound projector (Fig. 9), which incorporates all the 
features of the silent model, such as provision for 1000-ft. reels and 
film-conditioning during projection. In addition, the sound model 
is equipped with a dual amplifier giving an undistorted output of 
25 watts and a quality of sound reproduction that has been heretofore 
unavailable in the 16-mm. field. The amplifier and projector are so 




FIG. 8. Optical reduction sound 
printer ( R CA Manufacturing Co.). 



18 



PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. p. E. 



constructed as to permit the use of one or two projectors without 
changing the internal wiring of any of the components. Voltage 
adapters are incorporated in the amplifier to compensate for differ- 
ences in photocells, enabling projectionists to operate either projector 
without changing the volume control setting. The amplifier is 
designed to permit the use of a wide variety of microphones, such 
as carbon, velocity, crystal, or magnetic, without any alteration of 
the amplifier. The volume control is arranged to permit mixing 
sound records on the film and adding comments through the micro- 
phone. 

To popularize 16-mm. sound-film further, Victor Animatograph 




FIG. 9. 1000- watt Filmosound projector for 16-mm. film (Bell & Howell Co.) . 

Corporation has announced the Victor projector, model 25. In 
designing this equipment Victor is again pioneering in the develop- 
ment of high-quality but moderately priced sound equipment. This 
new projector, while not having the power of the model introduced 
last year, is sufficiently powerful for average school and home use. 

Andre Debrie, Inc., have recently introduced in America their new 
16-mm. sound projector. This projector has been widely advertised 
and has been favorably accepted abroad. 

Agfa introduced abroad the Mo vector Super 1 6 in a new sound model 
adaptable for either 110 or 220 volts a-c. The projector represents 
the latest development as to screen illumination and sound reproduc- 
tion. 

The Berndt-Maurer Corporation is now offering complete sound 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 



19 



recording equipment for 16-mm. film, including monitor and micro- 
phone, designed to work with a microphone as well as with direct 
pick-up from an amplifier. The complete unit is very compact. 

(6) Color. The outstanding event in the amateur motion picture 
world during 1935 was represented by the introduction of the Koda- 
chrome Process in April by the Eastman Kodak Company. This is 



Raw Film 

Emulsion 

Blue-sensitive 
Green-sensitive 

Red-sensitive 




Color Positive 

Yellow image 
Magenta image 

Blue-green image 




Anti-halation 
backing 



FIG. 10. Cross-section of Kodachrome 
film (Eastman Kodak Co.). 

a process of amateur cinematography in colors. It is a three-color 
subtractive process, the dyed images being incorporated in coatings 
upon one side of the film. It has an advantage over earlier amateur 
motion picture color processes in that the image is not broken into 
small units by screen elements or lenticular embossings. 

In the Kodachrome Process the film is coated upon one side with 
five layers. Next to the support is a red-sensitive emulsion; upon 



20 PROGRESS IN MOTION PICTURE INDUSTRY [j. S. M. p. E. 

this, a layer of gelatin; then, a green-sensitive emulsion; then, 
another layer of gelatin ; and upon the top, a coating of blue-sensitive 
emulsion (Fig. 10). The upper layer carries a yellow screening dye 
to prevent the blue light from reaching to the two lower emulsions. 
The film is exposed in any 16-mm. camera at approximately one 
stop larger than used for black-and-white pictures, without niters 
or other attachments, and can be run interchangeably with black- 
and-white film without any appreciable loss in screen brightness. 

In processing, the images are developed by a reversal process which 
converts them into positive dye images that are complementary in 
color to the spectral regions to which the layers respond. Processing 
can be done only in the stations of the Eastman Kodak Company. 
The film is supplied in 50- and 100-ft. spools, and in magazines, and 
in 16-mm. width only. 

(7) Miscellaneous Equipment. A new exposure meter of the 
photoelectric type was announced by Photo-Utilities. This new 
photoscope incorporates a mirror to reflect light to the sensitive cell. 
Greater sensitivity is claimed for this meter. Weston also has an- 
nounced a new meter having increased sensitivity. 

A continuous contact-printer of both silent and sound 16-mm. 
film has been designed by the Fried Camera Company of Hollywood. 
The new printer is compact and simple in operation, and a semi- 
automatic light-change is provided. 

Bell & Howell have made 400-ft. magazines available for Filmo 
70 cameras. This magazine is identical in construction to the Bell & 
Howell 35-mm. magazine which has been standard in the professional 
studios for many years. 

(II) SOUND RECORDING 

(1) General. The past year has been marked by a renewed 
interest in improving both sound recording and reproduction. The 
invalidation of the Tri-Ergon patents by the U. S. Supreme Court 
opened the way for intensive development of sound equipment which 
had been barred previously by the claims of these patents. 

At the S. M. P. E. Convention at Hollywood (May, 1935) a demon- 
stration of push-pull, variable-density recording was given by Douglas 
Shearer, of the Metro-Goldwyn-Mayer Studios. The sound was 
projected with the Fletcher two-way horn system previously de- 
veloped for the binaural transmission of music from Philadelphia to 
Washington. At the same Convention J. A. Miller demonstrated the 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 



21 



mechanographic method of recording sound upon film. Metro- 
Goldwyn-Mayer used the push-pull method for all original recording 
at the studio during the past year, re-recording to standard width 
track for the release prints. 

(2) Recording Equipment. RCA announced that several improve- 




FIG. 11. Sound recording stage dolly (RCA Manufacturing Co.). 

ments had been made in their studio sound recording equipment 
during 1935. A light-modulating system was produced and installed 
in several studios which utilized a beam of light only Ve of a mil thick 
for exposing the film. An improvement in the efficiency of the optical 
system and a new recording lamp made it possible to realize the in- 
crease in high-frequency response and the reduction in distortion. 



22 PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. P. E. 

The recorders are equipped with apertures for either push-pull or 
single-track recording. 

New amplifiers and control equipment have been designed which 




FIG. 12. Dolly-mounted portable ERPI recording system : (a) front view; 
(6) rear view (Paramount Productions, Inc.). 

more completely fulfill the requirements for flexibility as to mounting 
and arrangement for either studio, booth, or truck installations. The 
mounting racks may be placed against a wall, as all parts are acces- 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 23 

sible from the front, all panels are hinged so as to open toward the 
front, and all the parts are mounted upon the panels. The same 
equipment is suitable for stage mixing with high-fidelity phones 
(Fig. 11). 

Electrical Research Products, Inc., announces a new Western 
Electric portable recording system. This equipment has been de- 
signed with sufficient flexibility to fulfill requirements both in the 




FIG. 13. Re-recording machine (Electrical Research Products , Inc.). 

studios and on location, and to permit interconnection with existing 
equipment if desired. 

The new items of equipment comprising these stage units of the 
"tea-cart" or "dolly" type are (7) the pick-up unit, which, briefly, 
consists of the necessary pre-amplification, four mixer positions, and 
an over-all volume control ; (2) the main amplifier, providing separate 
outputs for recording and monitoring; and (3) an a-c. power con- 
version unit, which may be used in lieu of batteries (Fig. 12). 

With this arrangement all transmission adjustments are controlled 
at the stage, the remainder of the routine operations being handled at 
the position of the recorder, where newly designed units consisting of 
the recording machine and associated controls for noise reduction 



24 PROGRESS IN MOTION PICTURE INDUSTRY fj. s. M. p. E. 

and the motor system are located. Inter-phone equipment is built 
in, and provision is made for extending this communication circuit 
to the attendant at the microphone boom. Three microphones of 
the non-directional type, recently developed by the Bell Telephone 
Laboratories, may be connected directly to the pick-up unit, and 
provision is made for a fourth microphone input to operate from a 
standard microphone amplifier. 

The stage unit may be operated as part of a stage booth equipped 
with loud speaker monitor or in the open, using head-phones. For 
the latter case, the Bell Telephone Laboratories have made available 




FIG. 14. Three-unit playback (Klangfilm, G.m.b.H.). 

new high-quality head-phone receivers of the moving-coil type. These 
receivers have a marked improvement in response at both high and 
and low frequencies, and thus serve as better critera of the final 
recorded results than receivers heretofore available. 

(3) Re-Recording and Playback Equipment. Electrical Research 
Products, Inc., have announced an improvement in Western Electric 
re-recording equipment in the form of a new re-recorder for film 
reproduction (Fig. 13). The machine employs a new type of film- 
moving mechanism that is comparatively free from flutter, is very 
stable in operation, and incorporates a number of features contribut- 
ing to ease of operation and maintenance. It is a self-contained 
pick-up unit for direct mixer input, as it contains all the necessary 
features of preliminary amplification as well as film equalization. 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 25 

It is adapted for use with either half -width or full-width 35-mm. film 
and sound-tracks of either the standard or double-track, push-pull 
type, and is provided with an automatic rewind device for convenience 
in operation. Initial installations of this machine have been at 
MGM Studios who were instrumental in contributing valuable 
cooperation from a practical operating standpoint. 

From Germany comes announcement of the Klangfilm multiple 
playback device, which promises to play an important part in play- 
back and re-recording technic. One or more sound-tracks may be 
played back synchronously, all the units being capable of being 
interlocked with a projector or a recording machine. The equipment 
is arranged so that any one of the units may be used alone. An 
interesting feature is the ability to play back either negative or 
positive films with the device, the only change being the movement 
of a simple lever. Another feature is the provision for rewinding 
the film without removing it from the machine, three rewinding 
speeds being provided. A view of the triple multiple playback unit 
is shown in Fig. 14, the whole assembly being constructed horizontally 
instead of in the usual vertical arrangement of film reproducing ap- 
paratus. Provision is made for 300-meter rolls and for film loops up 
to 100 meters long. The advantages claimed for this multiple play- 
back unit are (1) highest quality of sound; (2) simplicity of operation; 
(3) no film multilation ; (4) flexibility of operation. 

The scanning system in this playback is similar to that used in 
the Europa sound-film equipment. This movement is said to assure 
absolutely uniform motion of the film at the scanning point. The 
movement is illustrated in Fig. 15. 

(4) Testing and Miscellaneous. With the increased use of portable 
equipment for use on location and of mobile stage units in recording, 
Electrical Research Products, Inc., has recognized the need for com- 
plete and reliable testing equipment of the portable type. They 
have consequently produced a combined portable oscillator and 
transmission-measuring set capable of checking gain, frequency, 
and power characteristics of complete operating channels or compo- 
nent parts. The oscillator is variable over the range of 40 to 14,000 
cps., and the gain set will measure gains up to 120 decibels and losses 
to 10 decibels. Convenient matching networks are provided to 
simplify measurements of various types of circuits. The oscillator 
is useful also for making frequency test-films and for tuning light- 
valves. The equipment is mounted on a chasis in a single case, the 



26 



PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. P. E. 



total weight being 50 pounds, and may be operated with batteries 
or an associated a-c. power conversion unit weighing 22 pounds. 

Electrical Research Products, Inc., is making field trials of a new 
midget noise meter design coded as the RA-198 sound level meter, in 




Photocell 



Glass rod 




(c) 



FIG. 15. Scanning system of Klangfilm multiple play- 
back: (a) film guiding at scanning point; (b) reproducing 
system, with rotary film-track and glass rod; (c) path of 
the light-beam in the Europa equipment. 

which compactness and simplicity of operation are the outstanding 
features. According to present specifications, the outside dimensions 
will be approximately 6X9X4 inches. The microphone, of the 
moving-coil type, is mounted in the face of the instrument, which is 
intended to be held in the hand when operated. Accurate readings 
may be made quickly without special skill on the part of the operator. 
No external power supply or batteries are required. Levels from 40 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 27 

to 125 decibels on the standard ASA scale may be measured. This 
range includes everything from quiet street and office noise levels to 
the loudest noises encountered. The instrument is designed to have 
a relative response to various frequencies or pitches of sound like 
that of the human ear. 

The General Radio Company has announced several items of 




FIG. 16. Strobotac a portoble stroboscope with neon 
lamp (General Radio Co.). 

interest to the sound engineer. A beat-frequency oscillator covers 
a frequency range of 10 to 20,000 cps. Its power output is 2 watts, 
maximum. The voltage output is constant over the entire range, 
and the total harmonic distortion is less than 1 per cent. The 
oscillator is completely a-c. operated, and can be mounted either in 
the cabinet furnished or upon a standard 19-inch relay rack. A more 
complete description is given in the July, 1935, issue of the General 
Radio Experimenter. 



28 



PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. p. E. 



The new General Radio distortion-measuring instrument is direct- 
reading, employing a large pointer-type meter. It operates on a 
test-signal of 400 cps., and is intended for use also in measuring the 
noise level of audio-frequency circuits when no audio-frequency signal 
voltages are present. This instrument is designed for relay rack 
mounting. Although developed for use in the radio broadcasting 




9 * 



FIG. 17. 



Type 209 reproducer set for small theaters (Electrical Research 
Products, Inc.). 



industry, the distortion and noise meter is applicable to all types of 
audio-frequency testing. 

The General Radio Strobotac is a small portable stroboscope using 
a neon lamp (Fig. 16). Although designed primarily for rapid speed 
measurements, it can be used also for the stroboscopic observation of 
rapidly moving objects. It should prove to be a valuable tool in 
both manufacturing and servicing motion picture cameras. The 
larger Edgerton stroboscope, type 548-B, has been widely used by 
camera manufacturers. The Strobotac, being a low-priced instru- 



July, 1936 ] PROGRESS IN MOTION PICTURE INDUSTRY 29 

ment, may possibly extend the advantages of the stroboscopic tech- 
nic to servicing cameras and projectors. It will probably be par- 
ticularly useful in observing irregularities in the operation of sprockets 
and shutters. 

(Ill) SOUND AND PICTURE REPRODUCTION 

(1) Sound Equipment. Continued progress was noted during 
the past year in improvements in sound reproducing systems, atten- 
tion being given to the film motion and to extending the frequency 
range of reproduction by the introduction of novel horn designs. 




FIG. 18. Multi-cellular horn (Electrical Research Products, Inc.}. 

Electrical Research Products, Inc., has announced a new high- 
quality reproducer set which forms part of a low-priced system re- 
cently announced, and has been designed with particular attention 
to the requirements of the small theater, high quality, economy, and 
simplicity being emphasized (Fig. 17). 

The type 209 reproducer set, as it is designated, may be attached to 
the picture projector with unusual ease, as all gears or other forms 
of drive have been eliminated between the picture mechanism and 
the sound reproducer. This avoids difficult alignment problems and 
"shimming." Sprockets are not required in the reproducer set, as the 
film is propelled only by the sprockets of the projector mechanism. 



30 PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. P. E. 

The new kinetic scanner controls the film motion and prevents 
flutter. The scanning system includes a prefocused-base exciter 
lamp, a high-efficiency optical system, and a photoelectric cell of 
greatly increased sensitivity. A special transformer is included for 
connecting the reproducer set to the system main amplifier; no 
amplifier is required at the machine. 

The same company has also introduced horns of the "multi-cellu- 
lar" type, the fundamental principles of which were developed by the 
Bell Telephone Laboratories. The design known to the industry as 
the "Fletcher" horn is another great contribution to the art of loud 
speaker design (Fig. 18). One of the first public demonstrations of 
this apparatus was given before the National Academy of Sciences 
in Washington, D.C., on April 27, 1933, during a presentation of the 
reproduction in auditory perspective of orchestral music by the Phila- 
delphia Orchestra under the direction of Dr. Leopold Stokowski. 
The music of the orchestra in Philadelphia was reproduced at Wash- 
ington by means of a special system including the "Fletcher" horns. 
The system was described by F. B. Jewett at the meeting of the Na- 
tional Academy of Sciences, at Washington, D.C., in April, 1933. 21 
Another demonstration was presented at the winter convention of 
the American Institute of Electrical Engineers at New York on Janu- 
ary, 1934, at which time papers were read describing the theory and 
design of the new loud speakers. 22 The new designs introduced by 
ERPI have aroused great interest in recent demonstrations of high- 
quality sound-picture reproduction. 

The horns are divided into diverging rectangular sections which 
distribute the sound uniformly over prescribed vertical and horizontal 
angles, assuring faithful balance at all frequencies. A new receiver 
having an efficiency about 100 per cent higher than any unit hereto- 
fore produced has also been developed. One to four receivers may be 
attached to a horn. Special throats are employed for connecting 
the receivers to the horn; the spaces surrounding the diaphragms 
of the receivers are specially designed to couple the diaphragms with 
the air columns of the horn efficiently and without distortion. The 
total depth of the horn is about 40 inches, thus allowing practical 
and convenient backstage arrangement. 

RCA announces new high-fidelity, a-c. operated reproducers em- 
ploying the rotary stabilizer form of control, and having increased 
power output and optional speaker complements to suit the require- 
ments of individual theaters. 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 31 

(2) Projectors and Accessories. The past year has seen a definite 
trend toward high-intensity projection by theaters of small and 
intermediate size, replacing the low-intensity reflector arc which has 
been in almost universal use in theaters of these classes. This change 
in projection practice has been made possible by the development of 
the a-c. high-intensity and the Suprex projector carbons, together 
with improved lamps for their operation. Now that these new car- 
bons and lamps have placed high-intensity projection within economic 
reach, the smaller theaters are rapidly availing themselves of the 
advantages already demonstrated in that respect by the large down- 
town theaters, in which high-intensity projection lamps have been 
in use for a number of years. The theater-going public has definitely 
shown its preference for the improved quality of projection light, 
the superior projection of color features, and the higher level of 
general illumination that high-intensity projection makes possible. 

For some time there has been a demand by a number of the larger 
theaters for still more intense illumination than could be supplied 
by the 13.6-mm., high-intensity projection carbon operated at 120-130 
amperes. This demand has now been met by the development of a 
13.6-mm., super-high-intensity carbon adapted to steady operation 
over a current range of 140-190 amperes. At the upper limit of cur- 
rent this new super-high-intensity carbon provides 30 per cent more 
light than the regular 13.6-mm., high-intensity carbon. There is 
also a more uniform distribution of brilliancy across the face of the 
crater of the new carbon, resulting in less contrast in screen illumina- 
tion between the center and the sides or corners of the screen. 

The lamp companies have recently made available an 8-volt, 
2-ampere T-8 bulb sound-picture reproducer lamp of improved char- 
acteristics (Fig. 19). This lamp, in general, replaces the widely used 
8 1 /2-volt, 4-ampere lamp of similar dimensions. Its low current 
rating permits operating it on rectifier filter systems of relatively 
small size and weight. The proportions of the source are such that 
the lamp operates particularly well with reproducer optical systems 
incorporating cylindrical lenses as well as with those of the aperture 
type. The lamp is available with the standard single-contact bayonet 
base as well as with the new precision prefocus base. The prefocus 
base makes it possible to position the lamp correctly in the optical 
system by merely inserting it into its special socket. This is a par- 
ticularly valuable feature for portable and semiportable equipment 
when the usual skilled operators are not available. The lamp is 



32 PROGRESS IN MOTION PICTURE INDUSTRY fj. S. M. P. E. 

applicable also to a number of 16-mm. sound-picture projectors. 
In connection with their studies of various types of recording and 
reproducing lamps for sound-picture work, the engineers of the Lamp 
Department of the General Electric Company have developed a 
special form of microphotometer which makes possible the measure- 
ment of brightness distribution across the scanning-beam as well as 
the total scanning-beam brightness for various types of optical sys- 
tems and lamps. The General Electric Com- 
pany has also recently placed upon the market 
a compact, inexpensive foot-candle meter, 
which should prove valuable to theater servic- 
ing organizations for checking screen and audi- 
torium illumination, etc. 

Zeiss has brought out a new series of pro- 
jection objectives for theaters, 23 the focal lengths 
of which range from 120 to 180 centimeters. 
The mounts are either 80 or 100 millimeters in 
diameter. 

(IV) LABORATORY PRACTICE AND SENSITOMETRY 

Installations of the Bell & Howell production 
printer in release print laboratories greatly in- 
creased in number during the past year. The 
FIG. 19. 8-volt, . 5 

2-ampere sound re- RCA Manufacturing Company announces suc- 

cording lamp (Gen- ce ssful introduction of their 35-mm. to 16-mm. 
eral Electric Co.). . 

reduction sound printers in a number of labora- 
tories during the year. There is not much to report in the way of 
new practices or equipment in the field of sensitometric control. 

The Ninth International Congress of Scientific and Applied Photog- 
raphy was held at Paris, July 7 to 13, 1935, in the meeting rooms of 
the French Photographic Society. The organization of the Congress 
was undertaken by a Committee appointed by the French Photo- 
graphic Society, and included representatives of photographic, scien- 
tific, and technical bodies from many countries. 24 

The two problems that gave rise to the most discussion at the 
Congress were the standardization of methods of determining speeds 
and other characteristics of photographic materials for commercial 
purposes, and the standardization of the dimensions of 16-mm. sound- 
film. 

Sensitometry Standardization. The question of working out a 




July, 1930] PROGRESS IN MOTION PICTURE INDUSTRY 33 

method of determining speeds and other properties of photographic 
materials that will be satisfactory for international use has engaged 
the attention of the International Congresses over a long period of 
years. The problem is not simple, and it is not yet solved. At the 
previous Congress, in 1931, the German delegation proposed a method 
of measuring and describing speed that was later adopted as the DIN 
system. 

The chief characteristics of the German proposal for speed deter- 
mination consisted in the use of a step tablet in conjunction with a 
standard lamp and a shutter that gave an exposure of 1 / 2 second. 
Development was to be in a specified MQ formula and "optimal"; 
i. e., for the time that would give the maximum speed figure when the 
test-strip was measured. The speed figure was determined by noting 
the number of the step on the tablet that gave a step on the test- 
strip having a density 0. 1 higher than the fog. The number of this 
step over ten (written, for example, 21/10) was to be taken as the 
speed number, and called "degrees DIN." 

Objection to "optimal development" was practically unanimous 
among the countries other than Germany. So far as the evaluation 
of speed was concerned, the various methods considered in addition 
to the DIN proposal were (1) the inertia method, of which the H&D 
system was an example; (2) the threshold method, of which the 
Scheiner and Eder-Hecht methods are examples; (3) the use of the 
exposure required to give a certain gradient in the underexposure 
portion of the characteristic curve. 

The American Committee favored a method in which speed was 
determined by the exposure required to give a certain contrast 
(i. e., a certain gradient or slope of the characteristic curve) for certain 
conditions of development. It was argued that the thing that mat- 
tered was not the exposure required to give a particular density, 
but the exposure required to give a certain contrast in the shadows 
of the subject. They were, however, not prepared to make any 
recommendations about it at the moment, because it had not been 
tried out in practice to any great extent. One objection also was 
that it was not simple to carry out. This, however, was remedied 
by the description at the Congress, in a paper by L. A. Jones and 
M. E. Russell, of the Kodak Research Laboratories, of a simple piece 
of apparatus for determining speeds according to this system that 
was not more difficult to use than the instrument used for determining 
the DIN or other speeds. 



34 PROGRESS IN MOTION PICTURE INDUSTRY [j. s. M. p. E. 

(V) PUBLICATIONS AND NEW BOOKS 

A rather small number of new books was published during the 
year and no new periodicals were known to have been issued. The 
bulk of the new books were devoted to amateur cinematography. 

The Cinema Digest, omitted unintentionally from last year's re- 
port, is now in its second volume. It represents the official monthly 
organ of Local 666 of the I. A. T. S. E., Chicago, 111. 

Books of primary interest that have been published since the last 
report of the Committee (May, 1935) are as follows : 

(1) Motion Picture Almanac (1935), Quigley Publishing Co., New 
York. 

(2) Year Book of Motion Pictures (1936), 17th Ed., Film Daily, 
New York. 

(3) Kinematograph Year Book (1936), Kinematograph Publica- 
tions, Ltd., London. 

(4) Yearbook of the Cine- Amateur ( Jahrbuch des Kino-Amateurs- 
1936) edited by W. Frerk, Photokino Verlag., Berlin. 

(5) Publications from the Scientific Laboratory, Agfa Photo- 
graphic Division (Veroffentlichungen des wissenschaftlichen Zentral 
Laboratoriums, Agfa Photographischen Abteilung) Vol. IV, I. G. 
Farbenindustrie A.-G., Hirzel, Leipzig. 

(6) History of the Discovery of Photography; G. Pontonnide, 
translation by E. Epstean, Walker Engraving Corp., New York. 

(7) Photographic Developers (Fotografische Ontwikelaars) ; 
M. C. F. Beukers, Waltham, Jr., Delft. 

(8) The Photography of Colored Objects, 13th Ed., revised, 
Eastman Kodak Co., Rochester, N. Y. 

(9) Practical Photography and Cinematography, Vols. I III, 
edited by E. Malloy, Newnes, Ltd., London. 

(10) Bluebook of Projection; 6th Ed., F. H. Richardson, Quigley 
Publishing Co., New York. 

(11) Movie Making Made Easy; 2nd Ed., W. J. Shannon, 
Moorfield & Shannon, Nutley, N. J. 

(12) The Leica Manual; W. D. Morgan and H. M. Lester, 
Morgan and Lester, New York. 

(13) The Cine" Amateur's Workshop; D. C. Ottley, Newnes, 
Ltd., London; also by the same author, Practical Set Structure for 
the Amateur Cinematographer; Pitman and Son, London. 

(14) Making Better Movies; Revised Ed., A. L. Gale and R. C. 
Holslag, Amateur Cinema League, Inc., New York. 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 35 

(15) Film Titling; G. P. Kendall, Newnes, Ltd., London. 

(16) Cine Photography for Amateurs, 2nd Ed.; J. H. Reyner, 
Chapman & Hall, London. 

(17) Film for All (Der Film fur Alles); W. Kross, W. Knapp, 
Halle. 

(18) Film Acting; V. I. Pudovkin, translated from the Rus- 
sian by I. Montagu, Newnes , Ltd., London. 

(19) Study of the Chromatic Sensitization and the Desensitiza- 
tion of Photographic Emulsions (fitude de la Sensibilisation chroma- 
tique et de la Desensibilisation des Emulsions photographiques) ; 
A. Chariou, Gauthier-Villars, Paris. 

APPENDIX A 

General Field of Progress of the Motion Picture Industry in Great Britain 

General. In Great Britain, the cautious optimism apparent in 
1934 appears to have been amply justified by the year 1935, especially 
so far as the motion picture industry was concerned. The prestige 
of the local producers has been enhanced by the improvement in the 
quality of their output, and it is significant that there is now a widely 
approved demand in trade quarters that the restriction be removed 
requiring importing producers to offer a proportion of films of local 
origin. In the industry generally, the promise of the previous year 
has fructified, and upon all sides investors are busy with schemes 
and projects for reaping the potential harvest. Recently the in- 
terest of strictly orthodox financiers has been aroused by a thorough 
statistical investigation of the industry's possibilities. 

Photography. Color continues to interest the producers, and in 
this connection Publicity Films have found considerable scope for 
color in advertising films. Moreover, the formation of Technicolor, 
Ltd., and the proposal to erect a laboratory at Denham during 1936 
have given impetus to the color movement, and it is believed that 
at least one major studio may produce a color picture during 1936. 

With the increased demand, trick photography has received much 
attention locally, and the assistance of experts from other countries 
has been called in. Rear projection work has also been advanced, 
and one local studio, the Stoll, Cricklewood, claims to be able to 
produce results of an exceedingly high order. The system in use at 
this studio, developed by Desmond Dickinson, the chief cameraman, 
utilizes an arc taking a current of about 300 amperes. The light from 



36 PROGRESS IN MOTION PICTURE INDUSTRY [j. s. M. p. E. 

this arc is concentrated upon a specially cooled Bell & Howell camera 
gate by a 15-inch reflector, the gate and associated mechanism being 
located in a special sound-proof chamber having transparent sides. 
Cooling of the gate is effected by a blast of air chilled by being passed 
through a cooling bath of liquid air. The intense light enables the 
background to be projected upon a thick paper screen only four feet 
from the foreground, giving a brilliant, realistically positioned back- 
ground without any "hot spot." 




FIG. 20. Developing machine (Andre Debrie Co.). 

Laboratories. Several laboratories have now installed the photo- 
electric densitometers made by Watson & Sons, Ltd., and a total of 
four laboratories has now been equipped with Eastman type lib 
sensitometers. Owing to the introduction of Eastman Super X 
negative into the English studios, several laboratories have had to 
modify their developing machines slightly to allow for the longer 
development time required by this material. Most laboratories 
develop a normally exposed Super X negative to a gamma of about 
0.70, as compared to 0.65 for the supersensitive material. 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 



37 



Studios and Laboratory Equipment. Much interest has been 
aroused by the announcement of a new Debrie multiplex high-speed 
developing machine having a frictional film drive and working in day- 
light (Fig. 20). The new laboratories at Denham will be equipped 
with these units. The Debrie Company has also brought out a 
series of film reduction printers, each capable of producing two or 
more reduced prints at a time, 
the range including a continuous 
motion printer for producing 
16-mm. sound film. This firm 
has also produced a machine for 
printing one to five standard 
copies simultaneously from one 
or two single negatives. Vint en 
& Co., of Cricklewood, are about 
to present a new 16-mm. printer 
capable of printing at speeds up 
to 70 feet of film per minute, 
and having a synchronous auto- 
matic printer light. These film 
printers include a sloping slit 
at the printer point that filters 
out flutter or slip frequencies 
in excess of 50 cps. Vinten is 
also producing a new bi-pack 
magazine for color-film cameras, 
in which the reels are mounted 
side by side instead of one above 
the other, as in leading existing 
types. Another purely local de- 
velopment, made also by Vinten 
& Co., is a film-matting machine, with which scratches in film base 
can be eliminated. Messrs. Frank Brockliss have put out some very 
popular arc spotlights embodying their patented "Stellmar" optical 
system. This system is satisfactory for use with arcs operated by 
direct or alternating current; the feature of utilizing light from 
both carbons in the latter case producing a maximum efficiency and 
non-fluctuating illumination. 

Sound Recording Equipment. A feature of this field has been the 
development of condenser microphones by certain of the smaller 





FIG. 21. Sound-track produced by 
Visatone noiseless recording system 
(Technical & Research Processes, 
Ltd.). 



38 



PROGRESS IN MOTION PICTURE INDUSTRY [j. S. M. p. E. 



companies. A smaller microphone of this type with a compact 
single-stage amplifier has been evolved by Technical & Research 
Processes, Ltd. (Visatone), and a larger unit has been made by 
Midgeley & Harmer, Ltd., for the Ambiphone system. The Ambi- 
phone unit comprises forty untensioned small diaphragms arranged 
on a grid-like structure, and is said to be simple to manufacture, free 




FIG. 



Double-film preview attachment for 
projectors (RCA, Ltd.). 



from cavity resonance, and non-directional. The impedance of the 
Ambiphone unit is given as about two to five megohms, and the 
frequency-response range and sensitivity are claimed to be very satis- 
factory. New Ambiphone equipment has been installed at British 
International Pictures Studios at Elstree. 

The Visatone Company is introducing a new system of noiseless 
recording using an unbiased oscillograph. The sound-track (Fig. 21) 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 39 

is produced by moving the shadow of an edge of a shutter or mask 
to and fro about the center line of the sound-track by movement of 
the oscillograph mirror in the well known way; and, in order to reduce 
background noise, a toothed mask having teeth of unequal length 
and shaded off in density at their ends is interposed in the light-beam 
between the first-mentioned mask and the mirror. The mask is 
moved out of the light-beam as the sound volume increases, so that 
a gradually increased area of the sound-track is cleared and becomes 
available for modulation. 

The RCA Company has developed locally a new preview attach- 
ment for projectors (Fig. 22) . The attachment is built in the form of 
a clover leaf and replaces the lower Simplex magazine with very little 
modification. The same firm has also evolved an immediate play- 
back disk recording equipment using cellulose acetate coated alu- 
minum disks. 

Cinemas and Camera Equipment. On the theater side of the in- 
dustry, the generally healthy tone of the industry has been reflected 
accurately. Theater building continues at an increased tempo, 
about 120 new houses having been opened during the year. A test 
case for the prevention of the exhibition of non-flam substandard 
film in ordinary public halls was lost, and in the industrial districts 
exhibitors are complaining of free shows now being given in taverns. 
Statistics show that these performances draw a considerable number 
of patrons to the houses concerned and enormously increase liquor 
consumption. 

Industrial and Educational. The Gaumont Company has been 
very active in the educational field and has formed a special company 
(Gaumont-British Instructional, Ltd.) which has built new studios 
devoted entirely to the production of instructional films. An ex- 
tensive library of such films has already been prepared. The Gaumont 
Company has also produced a new 16-mm. talking picture equipment, 
of which there are four models, for use in schools and in the home. 

The Western Electric Company reports that more than 8000 spon- 
sored shows have been given through their road show service during 
the year. On the industrial side, business has been well maintained. 
The high-speed camera exploited by this Company in conjunction 
with Messrs. Kodak, Ltd., also continues to demonstrate its utility 
in the study of rapid mechanical movement. 

Amateur Field. Probably one of the most important factors affect- 
ing the amateur field has been what appears to be the set-back in the 



40 PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. p. E. 

development of television. This was heralded in 1934 as being nearly 
ready to be publicized upon much the same scale as early radio, and 
high hopes were entertained. However, during the year it became 
increasingly apparent that the expectations of the Selsdon Committee 
were not likely to be realized. Moreover, the attention of the library- 
forming companies to the rapid printing of newsreel films on sub- 
standard stock has also contributed to the topical value of home 
outfits. Films of such events as the wedding of H. R. H. Duke of 
Kent and of the Jubilee were available to borrowers while public 
interest was still at its height. 

Amateur film companies continue to flourish and expand, and there 
are now probably about 200 throughout the country. In this con- 
nection, the Marguerite Sound Studios, which are well known in the 
motion picture industry, are preparing a program to enable film 
societies to supplement their present film activities which are chiefly 
silent, so that they can produce and exhibit talking pictures without 
any more elaborate sound equipment than an electric gramophone. 

Broadcasting. The linkages between the broadcasting industry 
and the motion picture industry have developed and strengthened 
during the year. The British Broadcasting Corporation continued 
to use film subjects for broadcasting purpose, the broadcast version 
of the film Friday the Thirteenth being a notable example. Also, 
film recording for playback broadcasting is said to be becoming in- 
creasingly important; and Publicity Films, who have exploited that 
field, are planning to erect a new studio especially to handle the busi- 
ness obtained. On the technical side, the research work conducted 
by engineers of the British Broadcasting Corporation relating to 
studio construction is of interest, a valuable contribution to the avail- 
able information on acoustics having been made in a paper recently 
presented by H. K. Kirke and A. B. Howe to the Institution of Elec- 
trical Engineers in London. Valuable information is also being col- 
lected as to the capabilities of various direct-recording systems. For 
example, the Stille-Marconi system of magnetic sound recording and 
the Marguerite system of disk recording are being used for immediate 
playback recording in England, and it is reported that the Nublat 
system of recording by cutting through a film strip to obtain two 
oppositely phased records, is proving quite promising. 

In conclusion, it may be said that as a whole the British Industry 
has experienced a successful year and appears to be upon the threshold 
of a period of still greater prosperity. 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 41 

APPENDIX B 
General Field of Progress of the Motion Picture Industry in Japan 

During 1935 the production of motion pictures in Japan was quite 
active. The total footage and the number of pictures produced show 
an increase over 1934. Theater attendance increased in proportion, 
and new and better theaters were opened in the leading cities. Along 
with the introduction of better theaters, the status of motion pictures 
as entertainment has been gradually raised. The result has been a 
demand for better pictures. The leading studios have attempted to 
meet this demand, and in so doing have limited their production of 
features to the point at which they have found it necessary to buy 
more imported pictures and more productions from independent 
producers. The general trend in Japanese pictures has continued 
toward the so-called modern style, as opposed to the ancient style or 
costume play, although some of the best pictures of the year were of 
the classical type. 

Studios. With the advance of sound, production in Tokyo has 
increased to a great extent. Nikkatsu have built a large new studio 
in the suburbs of Tokyo, and Shochiku have moved from their 
quarters in Kamata farther out where they have more space and, 
incidentally, new quarters. P.C.L., a rather recent entrant into the 
motion picture field, put through plans for expanding their studio in 
the suburbs of Tokyo. 

The stages in Kyoto that were destroyed in the typhoon of 1934 
were replaced in 1935, and in most cases this meant the replacement 
of silent stages by sound stages. 

Studio Production. As mentioned previously, the total footage 
produced increased over that of 1934. Among the features 60 per 
cent were with sound. Although there was a much greater footage 
of silent pictures (counting shorts and quickies) produced than sound, 
due to the comparatively small distribution of silent pictures, at 
least 60 per cent of the pictures being shown at any one time were 
sound pictures. 

Sound Equipment. Nikkatsu have increased the number of 
Western Electric channels to three, and have been renting a fourth 
from another licensee. Shochiku have been continually increasing 
the amount of their own sound equipment, devised by Mr. Tsuchi- 
hashi. There is also one RCA channel in use at the Uzumasa Studio 
in Kyoto, and other smaller independent studios have either acquired 
or added to their sound equipment. Except for the Western Electric 



42 PROGRESS IN MOTION PICTURE INDUSTRY [J. S. M. p. E. 

and RCA equipment, the sound equipment in use has in the past 
employed flashing lamps, but during the past year several have 
changed to variable-width recording. It is reported that some light- 
valve equipment other than Western Electric is in use, but due to 
the secrecy that surrounds this equipment, it is not possible to state 
so definitely. 

Laboratory Equipment. There has been a considerable increase in 
the number of continuous machines in service both in the laboratories 
and the studios. J. O. Studios and Far East Laboratories, Ltd., have 
built new laboratories in the Tokyo district equipped with modern 
laboratory machinery. P. C. L. Studio has installed a continuous 
machine, and Shochiku is equipping the laboratory in their new Ofuna 
Studio with continuous machines. Other machines were either under 
consideration or in process of being installed at the end of the year. 

Technical Advancement. There has been a gradual increase in the 
use of sensitometric control in the laboratories, resulting on the whole 
in an improvement in quality. Sound quality in general has im- 
proved, following a course in this respect similar to that of sound in 
the United States. Development has been delayed due to a lack of 
equipment and money. Because of the relatively small distribution 
of pictures made in Japan, the returns per picture are correspondingly 
small, which means that there is little money available for investment 
in equipment. 

Distribution. The average number of prints per picture is about 
seven, which gives an indication of the limited distribution. Total 
theater attendance was in the neighborhood of 240,000,000, at an 
average admission fee of 20 sen. When this is compared with the 
turnover in the United States for about the same number of pictures, 
it is easy to understand why it is necessary to economize in film and 
equipment. 

Distribution branches have been established in Manchoukuo. 
Although to date these have not been a very great source of revenue, 
this market offers an opportunity for expansion of the very small 
export market for Japanese pictures. 

Theaters. There has been a steady rise in the number of motion 
picture theaters during the past ten years, until now there are well 
over 1500. Of these, more than 900 are wired for sound. During 
1935 there was quite an increase in the number of sound installations, 
and many theaters replaced their existing equipments with better 
ones. 



July, 1936] PROGRESS IN MOTION PICTURE INDUSTRY 43 

In Japan it has always been the custom to have present a com- 
mentator who explains the picture to the audience and, with silent 
pictures, often supplied some of the dialog, many of them being very 
clever at doing so. Every year, as talkies advance, their services 
become less and less necessary, and the disposition of these men is 
a problem that regularly confronts the big theater chains. Although 
there has been a gradual decrease in the number of these commenta- 
tors, there are still some 6000 persons listed at this occupation. 

Imported Pictures. There appears to be an increase in popularity 
of imported pictures, particularly in the cities. This has been due 
partly to a lack of first-class locally produced pictures. European 
pictures increased in proportion to the American product, 20 per cent 
of the imported pictures being European. This is the highest point 
they have reached during the past five years. 

Superimposed titles have come into general use as a means of 
explaining the picture to those who can not understand all the dialog. 
Several pictures were scored with Japanese dialog this past year, and 
caused much comment among the critics and the trade journals. It 
seems that many of those who go to see foreign pictures prefer them 
in the original tongue, while others enjoy being able to understand 
the speakers, which they can not do in the original. The argument 
has not been settled, but it is not likely that there will be much scoring 
done so long as imported pictures remain so popular in their original 
tongue. 

REFERENCES 

1 Amer. Cinemat., 16 (May, 1935), p. 208; Brit. J. Phot., 82 (May 3, 1935), 
p. 275. 

2 Amer. Cinemat., 16 (May, 1935), p. 186. LEAHY, W.: "New Emulsions for 
Special Fields in Motion Picture Photography," /. Soc. Mot. Pict. Eng., XXV 
(Sept., 1935), No. 3, p. 248; /. Mot. Pict. Soc. India, I (Aug., 1935), p. 18. 

3 Zeitschr. Tech. Physik, 16 (1935), No. 4, p. 109. 

4 Zeitschr. Physik, 97 (1935), p. 34. 

5 Phot. Ind., 33 (Feb. 27, 1935), p. 191. 

6 Photo-Kino Chem. Ind. (1935), No. 1, p. 3. 

T Bull. soc. franc. Phot., 22 (July, 1935), p. 156. 

8 /. Amer. Chem. Soc., 57 (March, 1935), p. 547. 

9 /. Franklin Inst., 219 (March, 1935), p. 255. 

10 Amer. Cinemat., 16 (Dec., 1935), p. 516. 

11 Amer. Cinemat., 16 (Jan., 1935), p. 8. 

12 ALTMAN, F.: "A Revolving Lens for Panoramic Pictures," /. Soc. Mot. 
Pict. Eng., XXIV (May, 1935), No. 5, p. 383. 

13 Deutsche. Opt. Wochenschrift, 55 (Dec. 30, 1934), p. 826. 



44 PROGRESS IN MOTION PICTURE INDUSTRY 

14 U. S. Patents 1,987,878; 1,998,704; 2,012,822; 2,015,491. British Patents 
419,522; 423,156; 423,468. 

is TuxTLE, F., AND McFARLANE, J. W. i "Introduction to the Photographic 
Possibilities of Polarized Light," J. Soc. Mot. Pict. Eng., XXV (July, 1935), No. 
1, p. 69. 

16 Amer. Cinemat., 16 (Sept., 1935), p. 374. 

17 Zeitschr. wiss. Phot., 34 (1935), No. 1, p. 119. 

18 Camera (Dublin), 14 (July, 1935), p. 633; Amateur Phot. & Cinemat., 80 
(Aug. 21, 1935), p. 191. 

19 Phot. J., 75 (Jan., 1935), p. 28. 

20 Vero/ent. wiss. Zentral-Lab. Abt. Agfa, 4 (1935), p. 151; Ibid., p. 177. 

21 JEWETT, F. B.: "Perfect Quality and Auditory Perspective in the Trans- 
mission and Reproduction of Music," Science, 77 (May 12, 1933), p. 435. 

22 Electrical Engineering, 53 (Jan., 1934), p. 9; Bell Syst. Tech. J., 13 (April, 
1934), p. 239. 

23 Kinotechnik, 17 (May 5, 1935), p. 1471. 

24 /. Phot. Soc. Amer., 1 (Dec., 1935), p. 3. 



A STUDY OF THEATER LOUD SPEAKERS AND THE 

RESULTANT DEVELOPMENT OF THE SHEARER 

TWO-WAY HORN SYSTEM* 



JOHN K. BILLIARD** 

Summary. A description of recent "work carried on to study and formulate re- 
quirements to be met by the sound systems of motion picture theaters in order that the 
reproduction may be of a quality consistent with the recording technic available for 
some years to come. After setting up requirements relating to sound equipment; 
load capacitites; efficiency; volume ranges; transient, phase, and attenuation distor- 
tion; horn distribution characteristics; size; weight; costs; etc., the paper goes on to 
describe the design, installation, and performance, of the Shearer two-way horn sys- 
tem, engineered to meet the high standard of performance set up. The material of the 
paper is useful not only in connection with motion picture sound systems but also with 
public address systems and home radio equipments. 

INTRODUCTION 

The present investigation was undertaken with a twofold purpose 
in mind: first, to study thoroughly the more important types of 
extended-range loud speaker systems in current use, and second, to 
develop, if possible, a system which would combine practicability for 
theater use with as great an improvement in quality and efficiency 
as could be attained without greatly increased cost. The first objec- 
tive necessarily involved an effort to learn as much as possible of the 
"why" as well as the "how" of the systems and individual speakers 
studied, while the second led to considerable investigation of certain 
aspects of loud speaker design, some of which at least in the litera- 
ture of the subject seem not to have been sufficiently emphasized 
in the past. 

Any investigation of as wide scope as the present one would inevi- 
tably furnish many facts not pertinent to the main issue, but useful in 
other fields. The main body of the paper, however, has been written 

* Reprinted from the Technical Bulletin of the Research Council of the Acad- 
emy of Motion Picture Arts & Sciences, Hollywood, Calif. (March 2, 1936). 

** Transmission Engineer, Sound Department, Metro-Goldwyn-Mayer 
Studios, Culver City, Calif. 

45 



46 J. K. HlLLIARD [J. S. M. P. E. 

with the problem of the reproduction of sound for motion pictures 
ever in mind, and should be read from that viewpoint. It is felt, 
however, that the results referred to may form a definite contribution 
to other fields, such as public address work and home radio. 

SOUND REPRODUCTION SYSTEMS FOR MOTION PICTURE THEATERS 

The art of reproducing sound in motion picture theaters is now 
about eight years old. During this time there has, of course, been 
considerable improvement, but there has been only one major 
change in the standard theater installation. This change was the 
adoption of the wide-range 1 and high-fidelity systems after 1933. 
The principal modifications involved were : first, a partial fulfillment 
of greatly needed increase in amplifier carrying-capacity ; second, the 
adoption of speaker systems which provided for the division of power 
between two or more groups of speakers, each operating over a limited 
frequency range; third, improvements in the sound-head which re- 
duced flutter. While these improvements considerably raised the 
standard of reproduction in the theater, it was felt that the loud 
speaker system still constituted the principal limitation to natural- 
ness of reproduction. An investigation was accordingly made to 
determine whether a speaker system could be developed which would 
economically replace the present systems while providing the much- 
needed increase in fidelity. This was found to be the case, and it is 
the purpose of the present paper to describe this system and the 
results obtained with it, and to compare it with previous systems. 

Since it was not known how great a departure from a full-range 
linear response could be tolerated for the purpose in hand, it was con- 
sidered advisable to start with a system as near this as so far achieved, 
even though the form of apparatus available would by its size and 
cost prohibit its use for theater installations. From this it was de- 
terminable how much deviation was allowable and necessary in order 
to obtain a commercially practical system. Such a linear system was 
made available, 2 and a series of tests led to the following specifica- 
tions, which were found to be adequate for theater reproduction, tak- 
ing into consideration further developments in recording which may 
be expected within the next few years. 

SPECIFICATIONS 

Flat Over- All Frequency Characteristic. The system shall not deviate by more 
than 2 db., from 50 to 8000 cycles over the entire angle of distribution within 
ten feet of the mouth of the horn. 



July, 1936] THEATER LOUD SPEAKERS 47 

High Electroacoustical Efficiency. This shall approach 50 per cent in order that 
the required amplifier capacity need not be too great. 

Volume Range. The volume range shall be at least 50 db., and preferably 60 
db. 

Cost. This should be reasonable. 

Absence of Transient Distortion and "Fuzziness." The electroacoustical trans- 
ducer shall be of such construction that it shall not generate objectionable har- 
monics up to the peak power required, and the phase delay between units shall 
be such that the sound will be equivalent to that coming from a single source. 

Suitable Angular Distribution Characteristics. The sound shall be radiated 
through a horizontal angle as great as 110 degrees and a vertical angle of 60 de- 
grees, with nearly uniform response at all positions. 

Reasonable Compactness and Portability. Low weight. 

Amplifier Capacity. The installed amplifier capacity shall be such that one 
acoustic watt per 1000 square feet of floor area can be delivered when the audi- 
torium is adjusted for optimum reverberation time. 

A system which will conform to or exceed these specifications has 
now been developed, and can be constructed at moderate expense. 

In order to take advantage of these characteristics it has been 
found that when film is reproduced over a system such as this, it is 
necessary to keep the flutter from the sound-head no greater than 
0.1 per cent. Although the problem of flutter has been satisfactorily 
solved, and heads are commercially available which will pass the 
0.1 per cent flutter specification, it should be pointed out that by far 
the largest majority of heads in use today will not meet this specifi- 
cation. 

POWER AND FREQUENCY REQUIREMENTS 

The history of the electrical reproduction of sound has been one 
of continual increase in amplifier carrying-capacity, and in this re- 
spect the theater installation is no exception. 3 Originally, output 
powers from 2.5 to 12 watts were considered adequate for most houses. 
With the advent of the later systems now in use, these powers were 
recommended to be increased irom 3 to 6 db. depending upon the 
size of the house. It has been found from this investigation that it is 
both practical and eminently desirable to make a further increase 
of at least the same amount. The figure given of one acoustic watt 
per 1000 square feet of floor area is felt to be the minimum which will 
do justice to the advanced conception of reproduction with modern 
recording technic. It is of interest to note that this figure can be 
achieved allowing for considerable latitude above this point without 
danger of mechanical damage to the units. 

The advisability of extending the frequency-range of a reproducing 



48 J. K. MILLIARD [j. s. M. p. E. 

system must be determined by balancing the gain in naturalness, 
obtained by the extension, against the resulting increase in noise and 
extraneous sounds. In the present state of the recording art, a char- 
acteristic flat to 6000 cycles is the least that will do justice to the film; 
an extension to 7000 or even 8000 cycles is advisable, and a further 
extension is not. This is so because a further extension becomes of 
less and less value, due to the decreasing sensitivity of the ear and the 
small amount of energy in this region, and especially because above 
8000 cycles, noise, flutter, and harmonics due to recording deficiencies 
become decidedly the limiting factors. Incidentally, since practically 
all recording systems include a low-pass filter with a cut-off in the 
neighborhood of 8000 cycles, there is nothing on the film at high 
frequencies to be reproduced. 

Once the high-frequency limit is chosen, the low-frequency limit 
is automatically fixed. It has been found that for ideal balance the 
product of the two cut-off frequencies must be fairly close to 400,000, 
so that for an 8000-cycle upper cut-off, the lower becomes 50 cycles. 

HIGH-FREQUENCY HORN 

One of the principal limitations of present theater installations is 
the bad directional characteristic. The plain exponential horn has a 
directivity which varies with frequency; low-frequency sound is pro- 
jected fairly uniformly over a wide angle, but as the frequency is 
increased this angle decreases rapidly until at frequencies of several 
thousand cycles practically all the energy is emitted in a narrow 
beam. The result of this is that the reproduction becomes very 
"drummy" or "bassy" for that portion of the audience whose seats 
lie well off the axis, while the opposite is true for seats located di- 
rectly on the axis. In the present system this effect is eliminated by 
using a radiating system for the high-frequency unit which is com- 
posed of a cluster of small exponential horns, each having a mouth 
opening of approximately 60 square-inches. These individual units 
are stacked in layers to form a large horn, the mouth-opening of 
which is spherical in shape. The principle of this high-frequency 
unit can best be illustrated as a further compacting of the typical 
cluster of loud speakers, as customarily used in auditoriums and sta- 
diums for public address systems and announcing, except that the 
whole array is fed from a common header and driven by two dynamic 
units. This type of high-frequency radiation is also a feature of the 
aforementioned reference system. 2 However, the reference horn, 



July, 1936] THEATER LOUD SPEAKERS 49 

having been developed to a very limited angle and being driven by a 
single mechanism, was not adaptable to theater use as more than one 
horn became necessary for full coverage. This would result in non- 
uniform distribution as well as complete loss of coverage for a large 
part of the auditorium, should one unit fail during a performance. 

One of the features of the reference system is the use of a single 
diaphragm to reduce phase distortion. Inasmuch as theaters require 
parallel operation as protection in the case of failure of one unit, 
experiments were made with a F-throat and two units. As a result 




FIG. 1. The F-throat. 

of these experiments, it is now recognized by all concerned that any 
increase in phase distortion which may be introduced by the F-throat 
is negligible. 

The diaphragms are made of duralumin 0.002 inch thick and 
have an area of 6 square-inches. The diaphragm is mounted on the 
back of the assembly, and by the use of an annular opening, 2 the sound 
that is admitted to the throat within the unit has minimum phase 
distortion (Fig. 2). This is still further reduced by making this 
throat exponential, beginning at the annular opening, and avoiding 
the sharp discontinuity that may exist with a tubular throat. Two 
units are connected by means of a F-throat to the multi-channel horn 



50 



J. K. MILLIARD 



[J. S. M. p. E. 



which tends to reduce the distortion of high throat-pressure. The 
field excitation requires 25 watts per unit. 

The directional characteristics of the resulting unit are very satis- 
factory as found in theater installations. It should, perhaps, be em- 
phasized that lack of good distribution can not be corrected by equal- 
ization in the electrical circuits, since for any given adjustment, the 
over-all response is a highly varying function of position in the house. 
Although the characteristic can be made flat for any given position, it 




FIG. 2. Lansing No. 284E high-frequency unit. 

can not be made so for all or even a large part of the house by this 
method. 

LOW-FREQUENCY HORN 

In the case of a low-frequency unit, a suitable driving mechanism 
was not available, and it became necessary to develop one. The unit 
finally adopted consisted essentially of an exponential horn with a 
mouth area of 50 square-feet, and an axial length of 40 inches, driven 
by four 15-inch dynamic units of special design. The mouth opening 
was extended laterally to form a flat baffle 10 X 12 feet. The paper 
cones are dipped with lacquer to prevent them from absorbing mois- 
ture, which would vary their response. They are connected in series- 



July, 1936] 



THEATER LOUD SPEAKERS 



51 



parallel to give a desirable impedance characteristic as well as pro- 
viding insurance against complete failure of the system in the event 
that any individual unit should fail. The angle of distribution is 
uniform through an arc of 50 degrees on each side of the axis. The 
use of a horn instead of a flat baffle-board for low frequencies has 
several advantages. The efficiency is raised from 10 or 15 per cent 
to better than 50 per cent, which effects an enormous reduction in 
amplifier capacity. Undesirable radiation from the rear of the unit 
is considerably reduced and, as a result, the usual objectionable back- 
stage low-frequency "hang-over" is decreased to a negligible amount. 1 
For further compactness and rigidity, the low-frequency horn may 
advantageously be folded, and in this form retains the same charac- 



FIG. 3. 



Output characteristic; Shearer horn system, 
on normal axis, 10 inches from horn. 



Measured 



teristic if the air-path length be maintained unchanged. This modi- 
fication was contributed by H. F. Olson of RCA Manufacturing Co. 
The loading provided by the air column of the horn decreases the ex- 
cursion of the diaphragms as compared to the excursion necessary to 
produce equivalent output from a flat baffle array, and distortion is 
correspondingly reduced (Fig. 3) . 

With the low-frequency horn length as specified in the design un- 
der discussion maintained approximately equivalent to the length of 
the high-frequency horn, there is no time delay between the com- 
ponent sounds from the two horns. 

HORN ASSEMBLY 

The folded horn is assembled in sections, each section containing 
two driving mechanisms. They may be stacked one upon the other, 



52 



J. K. MILLIARD 



[J. S. M. P. E. 



depending upon the number required. Each section is adequate for 
an output from the amplifier of 25-30 watts for the required minimum 
harmonic content. If it is desired to secure a wide lateral distribu- 1 
tion the sections may be placed side by side. Section AA, Fig. 4, 
shows the construction of the horn. 

The entire horn is assembled so that the center of the high-fre- 
quency unit is approximately 50 to 60 per cent of screen height. This 
position has been found by years of use to be the center of activity or 
"presence" on the screen, and since the high frequencies are respon- 
sible for determining the "presence," the unit was so arranged. In 




HIGH FREQUENCY 



// 



\\ 



\. 



I'M 






FIG. 4. Shearer two-way horn system ; folded type. 

order to restrict the sound as nearly to a point-source as possible, the 
low-frequency horn is maintained at a position near the high-fre- 
quency horn (Fig. 5). 

The complete assembly is a unit so that it can be moved away from 
the screen or raised and lowered with the screen with minimum effort. 
The use of sections for the low-frequency horn allows the horn to be 
shipped and moved into spaces which have standard size doors. 



DIRECTIVITY 



For both the low- and the high-frequency units a certain amount of 
directivity is desirable. For most houses there should be but little 
energy radiated at angles greater than about 45 degrees from the 



July, 1936] 



THEATER LOUD SPEAKERS 



53 



axis, since such energy will be reflected from the walls and since for 
the best illusion the ratio of direct to reflected sound should be as high 
as possible. 

There is one additional consideration with regard to directivity 
which should be mentioned. Dr. V. O. Knudsen 4 has shown that at 
the higher frequencies, e. g., at 10,000 cycles, absorption of the at- 




FIG. 5. The folded-horn assembly. 

mosphere may become very serious, being as great as 0.2 db. per foot 
under certain conditions of humidity and temperature. In large and 
deep houses this would result in a serious loss of high frequencies in 
the rear seats. This effect can be considerably reduced by increasing 
the high-frequency radiation from those horns of the unit which serve 
these seats. It may be done by putting a suitable amount of absorb- 
ing material in the other horns and re-equalizing to bring the over-all 
response up to standard for the front seats. These artifices will 
probably not be required in most houses. 



54 



J. K. HlLLIARD 



HARMONIC CONSIDERATIONS 



[j. a M. p. E. 



One major defect of commercial loud speakers is their large ampli- 
tude distortion. One of the striking improvements in the new system 
is its "cleanness" of reproduction at low frequencies. The measured 
harmonic content is less than 4 per cent at 40 cycles, for 30 watts' 
output. This is due in large part to the use of a thick and com- 
paratively soft cone which can be driven to full excursion without 
break-up and consequent harmonic production. It was found by 
actual listening tests that with a pure tone of 40 cycles impressed, 




FIG. 6. Single-section, low-frequency folded horn with 52-degree 
high-frequency units, for use in studio viewing rooms and small 
theaters. 



most of the cone speakers investigated gave a greater apparent loud- 
ness than the speaker finally adopted. However, when a direct com- 
parison was made by keying the amplifier from the new unit to the 
unit under test, it was at once obvious that the output of the new one 
was fairly pure 40-cycle tone, while that of the other speakers con- 
sisted of, in most cases entirely, the second and higher harmonics. 
Direct measurement of the acoustic output showed that, in spite of its 
low apparent loudness, the fairly pure output of 40 cycles was actually 
about 6 db. higher than that of the other speakers. 

This great increase in apparent loudness due to transferring part 
of the fundamental power into harmonics in the conventional speaker 



July, 1936] 



THEATER LOUD SPEAKERS 



55 



is very striking, and is undoubtedly the explanation for the alleged 
high efficiency of many present-day speakers of all types. The loud- 
ness of the harmonics is not due to the rapid change in the sensitivity 
of the ear at low frequencies, which would favor the harmonics at 
the expense of the fundamental, since it occurs also at fairly high 
frequencies where the sensitivity of the ear is varying in the opposite 
way with frequency. With one particular pair of units tested, the 
effect was more striking at 1000 to 2000 cycles than at any other fre- 
quency. It is equally great with complex sounds, such as speech 
and music, although here the change in quality is somewhat less with 



FROM 


64 MT 

AMPLIFIER 
TPUT 


TO L 
1201 


4 TO ft OHMS 
>MH 


12 O 



X 



FIG. 7. Series type dividing network; Shearer horn system. 

respect to the change in apparent loudness than in the case with pure 
tone. 

PHASING 

Another important advantage of the new system is that it can 
easily be made to fulfill the requirements that the virtual sources of 
all the components of the reproduced sound shall coincide in the ver- 
tical plane. This condition is impossible to attain with divided-fre- 
quency-range systems now in use, in which the axial lengths of the sev- 
eral types of horns in a given system are widely different. In this re- 
spect, a two-unit system is much easier of adjustment than a three- 
way system. 1 It might be thought that since the time-delay is so 
small, of the order of a few milli-seconds, the effect would be inappre- 
ciable. This is true for certain types of sound, such as sustained 



56 J. K. MILLIARD [j. s. M. p. E. 

musical passages, but with dialog and especially certain types of sound 
effects which are of the nature of short pulses, a very objectionable 
distortion is usually noticeable. A striking demonstration of this fact 
was obtained by recording a tap dance. When this was reproduced 
it was found that the system with a very small time-delay afforded 
naturalness of reproduction, but that systems which had an appre- 
ciable delay reproduced the scene with far less realism. In fact, the 
sound did not appear to come from the screen, and, in addition, the 
tap was fuzzy in character, with a decided echo. 

This effect sounds somewhat like that of transient distortion due 
to the use of a filter with too sharp a cut-off, but it is actually more 
analogous to the echo effect often observed on long lines and with 
certain types of phase distortion networks. 

A recent paper 1 discusses the features of the three-way system in- 
cluding some of the limitations which require special installation 
technic for the setting of horns, backstage draping, phasing of vari- 
ous horn positions, position of horns for distribution, and setting of 
volume between horns. Familiarity with these data will assist in 
appreciating the principles of the present system. 

It should be pointed out that the over-all frequency response curve 
of the system should not fall off too rapidly beyond the cut-off fre- 
quencies, or objectionable transient distortion will result. Probably 
the maximum slope that can be tolerated is of the order of 20 db. per 
octave, or roughly, that of a single-section constant-^ filter. 

DIVIDING NETWORK 

The frequency chosen for the critical frequency of the dividing 
network is governed by several factors. If this frequency is too low, 
it leads to un economically large values of capacity in the network, 
and to impracticably large horns for the high-frequency unit. If too 
high, there is danger of running into the characteristic dip which 
seems always to be present in large cones ; and, also, it would result in 
dividing the prime energy of speech sounds between the two units, 
which is objectionable from the standpoint of good "presence." If 
the critical frequency is chosen as approximately 250 cycles, a good 
compromise results (Fig. 7). 

A dividing network was chosen which gave fairly rapid attenua- 
tion, 12 db. per octave, in order to keep any appreciable low-frequency 
energy out of the high-frequency unit, and to minimize the effect of 
irregularities encountered in the response curve above the designed 



July, 1936] 



THEATER LOUD SPEAKERS 



57 



range of the low-frequency cones. This lies somewhat above 400 
cycles for an efficient low-frequency unit. Certain dividing networks 
in current use have attenuation curves of such gradual slope that at 
some frequencies the irregularities in response of the speakers are 
actually greater than the attenuations of the network. 

The network is designed so that the reflected impedance of the 
horn on the amplifier is approximately 2.5 times the amplifier im- 
pedance. The loss in the network is less than 1 db., in order that the 
full capacity of the amplifier may be utilized. 

MEASUREMENTS 

While it is recognized that indoor response measurements do not 
have the degree of precision that may be had in free space, they 




FIG. 8. A typical individual channel. 

nevertheless do represent conditions under which the loud speakers 
must actually be used for motion pictures. Also, for the purpose at 
hand, comparative measurements are sufficient, and were verified by 
listening tests which, in the end, is the final criterion (Fig. 3 shows 
average response). 

Irregularities in the sound-pressure at the microphone due to 
standing-wave patterns in the room are minimized by the use of a 
conventional warble frequency, varying ==25 cycles at a 10-cycle rate. 
Tests have been run which indicate that the warble is effective only 
below 2000 cycles. Above this point, the standing waves do not in- 
terfere with the correct interpretation of the response curve. 

The measurements were taken in a stage 100 X 70 X 35 feet, hav- 
ing a reverberation time of one second at 512 cycles per second. By 
making the measurements indoors, tests could be made rapidly on a 
large number of units without the interference from outside noises, 
due to a 60-db. insulation between the inside and the outside provided 



58 J. K. MILLIARD fj. s. M. P. E. 

by the building. The response curves were measured using a high- 
speed level indicator 5 capable of responding to a change in level as 
rapid as 300 db. per second. 

Douglas Shearer, head of the Metro-Goldwyn-Mayer Sound De- 
partment, brought about and directed this project. This develop- 
ment was engineered by the writer and contributed by Metro-Gold- 
wyn-Mayer Studios. The cooperation of the following companies is 
gratefully acknowledged: Electrical Research Products, Inc.; RCA 
Manufacturing Co.; Lansing Manufacturing Co.; and Loew's, Inc. 
These companies assisted by making available test equipment, the 
reference system, and staff and theaters, which greatly facilitated the 
work and produced a coordinated result not otherwise possible. The 
writer wishes to acknowledge also the contribution of the Metro- 
Goldwyn-Mayer Sound Department, and, in particular, R. L. Ste- 
vens, who carried out the mechanical design. 

REFERENCES 

1 MAXFIELD, J. P., and FLANNAGAN, C.: "Wide-Range Reproduction in 
Theaters," /. Soc. Mot. Pict. Eng., XXVI (Jan., 1936), No. 1, p. 67. 

2 WENTE, E. C., and THURAS, A. L.: "Loud Speakers and Microphones," 
Electrical Engineering, 53 (Jan., 1934), No. 1, p. 17. 

3 WOLF, S. K., AND SETTE, W. J.: "Acoustic Power Levels in Sound Picture 
Reproduction," J. Acoust. Soc. Amer., II (Jan., 1931), No. 3, p. 384. 

4 KNUDSEN, V. O. : "The Effect of Humidity upon the Absorption of Sound in 
a Room," /. Acoust. Soc. Amer., Ill (July, 1931), No. 1 (Part 1), p. 126. 

5 WENTE, E. C., BEDELL, E. H., Swartzel, K. D.: "A High-Speed Level Re- 
corder for Acoustical Measurements," /. Acoust. Soc. Amer., VI (Jan., 1935), 
No. 3, p. 121. 

APPENDIX 

Low-Frequency Exponential Horn 

Fundamentally, the design of a low-frequency exponential horn follows the 
same treatment as that accorded a horn for high-frequency response. There is, 
however, a greater tolerance allowable in deviating from theoretically calculated 
values: namely, expansion rate (governing value of cut-off frequency), mouth 
size, and nature of cross-section. Discontinuities which would be out of the 
question in high-frequency design may be permitted with little loss in a low-fre- 
quency horn. Numerous tests have borne out the above statement. A horn of 
folded cross-section has been chosen for general use in this system, because it 
permitted a compactness of design not possible with a straight exponential horn. 
Sufficient loading has been obtained in a small space to permit the cone-driving 
units to operate at their optimum efficiency. 

For the purposes of illustrating the method of computation, a brief summary of 



July, 1936] THEATER LOUD SPEAKERS 59 

the calculations involved in the design of a straight exponential horn will be given : 
The cut-off frequency was chosen as 50 cycles per second. A 50-cycle wave has 
a length of 271 inches. The distance across the mouth of the horn should be 
equal to at least one-quarter of the wavelength of the lowest frequency it is desired 
to transmit. This value for the horn in question gives a minimum mouth size of 
68 inches. The size of throat must be sufficient to accommodate four 15-inch 
cone speaker units. A throat size of 30 X 30 inches was chosen. 

It has been found that an exponential horn whose area doubles every 12 inches 
will have a cut-off frequency of 64 cycles per second ; one whose area doubles every 
6 inches, a cut-off frequency of 128 cycles per second. From the above relation- 
ship the length for the area of the present horn to double may be found by the 
simple proportion 64/X = 50/12, from which X = 15.36 inches. From the 
general horn equation: 

A. = A e M * 

where: A x = Area at any point X 

Ao = Area of throat (chosen above as 900 square-inches) 
= 2.7183 

M = Flare constant of horn 
X = Distance along horn axis from throat 

M can be computed by substituting known values in the above equation : 

1800 = 900 X 2.7183 Ml5 - 36 
from which M = 0.045. Then the equation for the present horn becomes: 

A = 900e- 04 5* 
from which the sectional area at all points X may be computed. 

For a minimum distance across the mouth of the horn of 68 inches or a minimum 
mouth area of 4624 square-inches, the length is determined: 

A = 900e-* 
4624 = 900 X 2.7183- 04S 
where X = 3Q 1 / 4 inches. 

It has been found, however, that while the sizes given above are satisfactory 
from a theoretical standpoint, an increase in loading will result in a higher ef- 
ficiency. An increase in length to 44 inches with a corresponding mouth size of 
80 inches, or 6400 square-inches has, as a result of tests, proved to be perhaps the 
most desirable size. The over-all length, inclusive of units, then becomes approxi- 
mately 55 inches. This length is considerably more than is desirable for the 
majority of installations. 

The above analysis applies to the straight type of horn rather than the folded 
type. 

Fig. 4 illustrates a horn of folded cross-section. Here it is possible to retain 
optimum loading conditions in a minimum of space. It is, however, in this case 
mechanically impracticable to construct a horn of true exponential shape. 



60 J. K. HlLLIARD 

The mouth, throat size, and flare constant are determined as in the case of the 
straight exponential horn. Intermediate cross-sectional areas are approximated 
to those of a true exponential horn as closely as is feasible without involving con- 
structional difficulties. 

It has been found that the difference in response is sufficiently slight to justify 
this deviation from the theoretical. 

High-Frequency Exponential Horn 

The specifications require that the over-all depth or length of both low- and high- 
frequency assemblies shall not exceed 44 inches. 

This limitation of length brought about the selection of a theoretical cut-off 
frequency of 220 cycles per second. This value of cut-off allowed the design of 
a horn which fulfilled the desired requirements, such as a spread of either 90 or 
105 degrees with a maximum of six separate channels and a sufficient mouth size 
to present a reasonably small amount of discontinuity. 

By simple proportion, as before, the length for the area of the present horn to 
double may be found: Q4/X = 220/12, from which X = 3.5 inches. 

From the general horn equation, choosing V 4 square-inch for A , M can be com- 
puted by substituting the known values: 

V 2 = 1 A X 2.7183 3 ' 5:rAf 
from which 

M = 0.2 
Then the equation for the present horn becomes : 

A = V4' 2x 
from which the sectional area of the horn at all points X may be computed. 



DIVIDING NETWORKS FOR LOUD SPEAKER SYSTEMS* 
J. K. MILLIARD AND H. R. KIMBALL** 



Summary. A description of the theoretical and practical design of dividing net- 
works for use in coupling power amplifiers to loud speaker systems in which two sets 
of horns are used for reproducing the sound energy. Performance curves and de- 
sign data are given to facilitate the engineering of such networks. 

INTRODUCTION 

In the design of linear sound reproducing equipment wherewith 
it is desired to reproduce faithfully tones from about 50 cycles per 
second to about 8000 cycles per second, it is common practice to 
divide the frequency range into two or more parts, and to provide 
one or more loud speakers for each of these frequency ranges. The 
speakers employed for the different bands are, of course, differently 
designed, each speaker being particularly suitable for its own band. 
Since it is not possible to design speakers which will faithfully and 
efficiently reproduce frequencies in one pre-assigned band and sharply 
attenuate frequencies outside the band, it is necessary to supply an 
electrical network between the final power amplifiers and the speakers 
to deliver the correct frequency band to each of the sets of loud 
speakers. These networks have acquired the name of "dividing net- 
works." 

It is the purpose of this paper to discuss the theoretical and prac- 
tical design of such networks and to give data from which the elec- 
trical constants may be easily selected. Only two-way speaker sys- 
tems, that is, systems dividing the frequency band into two parts, 
are discussed. The theoretical information given, however, is funda- 
mental in nature and may easily be extended to cover three-way 
speaker systems. 

For the two-way system the speakers handling the lower frequencies 
are termed the low-frequency speakers or low-range speakers. In 

* Reprinted from the Technical Bulletin of the Research Council of the 
Academy of Motion Picture Arts & Sciences, Hollywood, Calif. (March 3, 1936). 
** Sound Department, Metro-Goldwyn-Mayer Studios, Culver City, Calif. 

61 



62 J. K. MILLIARD AND H. R. KIMBALL [J. S. M. p. E. 

like manner, the speakers having the job of reproducing the higher 
frequencies are called the upper-frequency speakers or upper-range 
speakers. For each of the two frequency bands one speaker unit or 
a number of speakers arranged in series-parallel combinations may 
be used, depending upon the impedance of the speakers. 

Dividing networks are not usually of the sharp cut-off type, that 
is, they are not arranged to transmit uniformly frequencies of a 
given band and sharply attenuate all other frequencies. Rather, 
they transmit the band frequencies almost uniformly, and gradually 
slope off, thereby allowing a certain amount of over-lap between the 
assigned frequency ranges. While theoretically it may seem de- 
sirable to arrange dividing networks to cut off sharply, from a com- 
mercial standpoint the sharpness of cut-off is necessarily a com- 
promise between expense and effectiveness. For well designed speaker 
systems, the rate of change of attenuation should at least be sufficient 
to suppress objectionable irregularities in the response of one horn 
in its transmitting range because of sound coming from the other 
horn in its suppression range. From an analysis of a large. number 
of speaker systems it appears that the dividing network should pro- 
vide at least 10 or 12 db. of attenuation one octave away from its 
cut-off. Concerning the maximum rate of change of attenuation 
which should be used, increased attenuation is accompanied by 
increased losses in the transmitting ranges which, for high-powered 
systems, at least, is to be avoided. Costs also may mount up un- 
reasonably if a large amount of filtering is employed. For these 
reasons and considering the magnitude of the irregularities which 
one speaker produces in the transmitting range of the other, it appears 
that few dividing networks should employ more attenuation than 
about 18 db. per octave. 

In a two-way system the frequency at which both sets of speakers 
receive equal amounts of energy is called the "cross-over point." In 
other words, the cross-over point is the point of separation between 
the two bands of frequencies. In developing speaker systems a trial 
cross-over point is usually arbitrarily selected, keeping in mind the 
characteristics of the upper- and lower-range speakers which are to 
be used, costs, and other items, and later moved one way or the other 
if found unsatisfactory when the system is operated as a whole. 
Where it is desirable to use a baffle board in connection with dynamic 
speakers for low-frequency range and a horn for the upper-frequency 
range, experience has shown that the cross-over point should be 



July, 1936 j DIVIDING NETWORKS FOR LOUD SPEAKERS 63 

placed near the lowest frequency the horn will safely transmit in its 
linear range, in order that the effect of time-lag between the low- and 
high-frequency speakers will be reduced over a large portion of the 
range. It is not economical to use too low a frequency, since large 
values of capacity are required in the dividing network and the 
high-frequency horn must be large to keep its cut-off low. In general, 
the division of the band for this reason should not be below about 200 
cycles. If the band division is at higher frequencies, such as 1000- 
3000 cycles per second, an irregular response due to dips in large 
low-frequency commercial cones is likely to occur. Also, if a small 
baffle-board is used, there is the orue inherent dip due to interference 
between the radiations from the front and the rear sides. From this 
it appears best to divide at some low frequency, 200-350 cycles, as 
most commercial cone speakers are reasonably flat up to this point 
and an excessively large high-frequency horn will not be required to 
transmit down to 200 cycles. 

GENERAL DESIGN THEORY 

A two-way dividing network consists of a low-pass filter and a 
high-pass filter designed to operate from a common source at their 
input ends. Two types 1 ' 2 ' 3 of such networks are in general use: 
namely, the shunt type, in which the input terminals of the two filters 
are in parallel; and the series type, in which the filters are connected 
in series at their input terminals. Different design methods are used 
for the two types, but as discussed later the types are inverse to each 
other. In arranging a low-pass and high-pass filter for series or paral- 
lel operation it is necessary to employ special design methods only 
in connection with the first half-filter sections of each of the filters, 
the remaining sections of the filters being designed in accordance 
with conventional filter practice. 2 For the first half -filter sections 
Af -derived types are used, the filters having mid-shunt terminations 
for parallel operation and mid-series terminations for series operation. 

Fig. 1 shows a low-pass filter and a high-pass filter, each of which 
has its first half -filter section shown in detail and the remaining filter 
sections in block schematic form. It is recognized that half -sections 
shown are each mid-shunt terminated Af-derived types, the constant 
M determining the place in the frequency range where infinite attenua- 
tion is theoretically attained and also controlling the frequency con- 
figuration of the mid-shunt image impedances as shown in various 
books describing filter design methods. 3 Without going into the mat- 



64 



J. K. MILLIARD AND H. R. KIMBALL [J. S. M. p. E. 



ter here it may be mentioned that a value of M equal to about 0.6 
gives image impedances over the passing bands that are sufficiently 
close to constant resistances for dividing network purposes. The 
filters shown in Fig. 1, when used individually and when the filter 
sections contained in the block schematics are designed according 



o 


XUUUL 






-} 






^il-rrv'Jk.l 


Low- 




Henrysj 


Pass 


X ^ 


i I "*" X 








Filter 


L_ 


-t---j r 


Section 









Z c .i * Image Impedance 
Ohms 




a ^R Vl~(7") 3 Mid-series Image Impedance 

c/ Ohms 



HIGH-PASS if Farads 



Z HJ = Image Impedance 
Ohms 





| | 










1 
1 


|^ ! 


High- 




Henrys, 


Rass 


X b 


| j (- ><bb 


filter 




J-i^A, 1 


Sections 


1 


C-T- Farads j J 






I 












R I" T = Mid-series Ima^e Impedance 
Ohms 

FIG. 1. (Upper) low-pass filter; (lower) high-pass filter. 

to conventional filter practice, should have reasonably good attenua- 
tion characteristics. 

In showing the changes that it is necessary to make in the terminat- 
ing sections of the filters of Fig. 1 to make parallel operation possible, 
it is interesting first to consider some of the reactive impedances of the 
filters at different points. In order to be specific, it is assumed that 
each of the filters is designed for a cut-off frequency of i c cycles per 
second, and that the low-pass filter has an image impedance of R 



July, 1936] DIVIDING NETWORKS FOR LOUD SPEAKERS 



65 



resistive ohms at zero frequency and the high-pass filter has the 
same image impedance at an infinite frequency. 

Fig. 2 shows the reactive impedances listed below for the filters. 
These reactive characteristics were calculated for a value of M equal 




FIG. 2. Reactance impedance characteristics of networks in Fig. 1. 

to 0.6, curves for other values of M not being included because of 
the confusion they would cause in the drawing. 

(1) Impedance characteristic in the passing band of the coil and condenser 
shunted across the input of the low-pass filter, designated in Fig. 1 as X a . 

(2} Impedance characteristic in the passing band of the coil and condenser 
shunted across the input of the high-pass filter, designated in Fig. 1 as X b . 



66 



J. K. MILLIARD AND H. R. KIMBALL [J. S. M. P. E. 



(5) Image impedance characteristic in the attenuation range of the low-pass 
filter at the point aa of the filter, designated as X aa . 

(4) Image impedance characteristic in the attenuation range of the high-pass 
filter at the point bb of the filter, designated as X 66 . 

It is seen that the reactive impedances of curves 1 and 4 are very 
nearly alike over the complete passing band of the low-pass filter, and 



Image Impedance 
Ohms 




-ft) 1 





Low 


J 


- m R^c3 Farads ' *- 


Pass 
Fdter 






Sections 


A 






High 




fe Henrys p~ 


Pass 
Filter 


o E \ 


Sections 


\ 



"R l- -f = Mid -series Image Impedance 
Ohms 



Mid-shunt Image Impedance 
Ohms 



Load 



Load 




SERIES 
TYPE 




'/ /p\2 = Mid-shunt Image Impedance 
VI ' (fl Ohms 

FIG. 3. Dividing networks : (a) parallel type; (&) series type. 

likewise the same is true of curves 2 and 3 over the passing band of the 
high-pass filter. This leads to the conception of placing the two filters 
in parallel by omitting the shunt coils and condensers at the input 
ends of the filters as in Fig. 3a. In other words, in the passing band 
of the low-pass filter, the filter elements of the high-pass filter take 
the place of the shunt coil and condenser; and conversely, in the 
passing band of the high-pass filter, the filter elements of the low-pass 



July, 1936] DIVIDING NETWORKS FOR LOUD SPEAKERS 



67 



filter take the place of the shunt coil and condenser omitted from the 
high-pass filter. Then in Fig. 3a the low-pass unit in its transmitting 
range should exhibit practically the same attenuation and impedance 



Parallel Type 
Dividing Network 



Series Type 
Dividing Network 



Input 


T 


Low 
r Frequency 
Speakers 




II , 


II' o 


II J 


11 High 
Frequency 
Speakers 



Input 

Q 




Low 

I Frequency 
Speakers 


1 fc- 


High 
Frequency 
Speakers 
o 



Input 


1-4 


E 


Low 
Frequency 
Speakers 






it 






^r^ 

L 


f 


High 
Frequency 
Speakers 



Input 


L, 


Low 
Frequency 
Speakers 




I? 




II 


H.h 
Frequency 

Speakers 



(e) 



Henrys 



Farads 



Input 


L|k Low 

- C 4 Frequency 
Speakers 


High 
;L - S Frequency 
C, Speakers 


U " 


Input 
o 


Low 
- Cj Frequency 
Speakers 


High 
Lj Frequency 
Speakers 



(f) 



FIG. 4. Dividing network designs. 

characteristics as the low-pass filter of Fig. 1, and likewise for the 
high-pass unit in its passing range. In the attenuation ranges of the 
filters the networks of Figs. 1 and 3a will not be respectively the same, 
but any lack of attenuation that the network of Fig. 3a has lost by 



68 



J. K. HlLLIARD AND H. R. KlMBALL [J. S. M. P. E. 



parallelling can always be made up by adding more sections in the 
block schematics. Fig. 3a then provides a method of designing the end 
half -sections of a low-pass filter and a high-pass filter where they are 
to be operated in parallel. 

The same procedure as described above could be gone through for 
arriving at the design of a low-pass filter and a high-pass filter which 
are to be operated in series. This, however, is not necessary, as the 
series type of network can be arrived at by using the principle of in- 
verse networks. The network of Fig. 3b is the inverse of the network 



M 


* 





tr> 


t* * Q 


* 2 1 1 ? 


n 


s 


h 


?S 


l 1 


I 


1 


S 


S 


! 


MIceOFAISADS 


IOOO 








L 


I C, C, 

If L . 


C, 

1-4 


I- 






















999 










\\ \ 


\ 


\ 




N 


OTE = rOK g, OTMEI? THAN 10 OHMS 
MULTIPLV INDUCTANCE RY */# 
OIVIQE CAPACITANCE BY *'/ lo 




tSXL 
TSS, 

too. 
roo_ 
4M_ 
900 


CUT-OFF FeCpUENCV 












\\ \ 




\\ 
















\\ 


\ 


\ 


\ 






























\\ 


\ 




V 
\ 






























\\ 


\ 




\ 


\ 




























\ 


\ 


\ 




\ 


\ 
\ 


\ 


























\\ 




\ 






\ 


s 












too 














^ 


\ 


\ 


\ 


S 


s ^\ 












too 
















x 


\ 
X 


X 




;<^: 


^ 










S 


| 


j 


S 


SJjjj 


MILLIHENerS 


s 


2 


g 


i! 


1 S 


o 

1 


O 

? 


o 

S 




5S 


ill! 


*2 al 3 * 



FIG. 5. Electrical constants for networks of Fig. 4: M = 
o = 10. 



0.6, 



of Fig. 3a, and represents the design procedure employed for placing 
a low-pass filter and a high-pass filter in series. The same value of 
M = 0.6 is, of course, used, since the networks are inverse to each 
other. 

SPECIFIC DESIGN 

The foregoing work has provided methods for designing the first 
half -filter sections of low-pass and high-pass filters of two-way divid- 
ing networks. As has already been mentioned, the number of filter 
sections that form the remaining parts of the network, as represented 
by the block schematics of Fig. 3, depends upon how rapidly it is 
desired to attenuate the suppressed frequency ranges; or, in other 
words, how much frequency overlap of the low-frequency range and 



July, 1936] DIVIDING NETWORKS FOR LOUD SPEAKERS 



69 



the high-frequency range is to be permitted. Where it is desired to se- 
cure an attenuation rate of change of about 18 db. per octave, one 
filter section for each of the block schematics of Fig. 3 is sufficient. 
Where an attenuation rate of change of about 12 db. per octave is 



o 

4 












^ 


s^ 


\>f 
















8 I* IN h 
[ NETWORK LOSS DB 




TERMINATIONS = e. 




/ 


\ 


NETl 


<JORKS fa) AW& (b) OF FIG. A 

PHASE DIFFERENCE 
AT CROSSOVER - 321 














/ 




\ 












/ 






\ 






























/ 








\ 






















24 3 


s 


? 





3 


g 


3 


g< 


] * I 


o 


o 





5 


o 


9 

c 


s 


e 








o 

4 












x 


N 


V 


2 
















*L 

^^ 3 
M 

l 1 

u 
eo 2 




TERMINATIONS -l? 




/ 




\ 


NETWORKS (c) AND (d) OF FI6. 4 
PHASE DIFFERENCE 
AT CeOSSOV/ER =221' 












/ 


y 






\ 










/ 










\ 




























/ 














\ 




















24 S 


g 


< 


8 


^ 


8 





s 





^ a 


\ Q 




^ 





o 
\s 







q 




5 


o 
2 


\ 






NETW.OPK5 fe) AND (U pF FIS 4 
PHASE DIFFERENCE AT 
ALL FREQUENCIES- 90" 



^> O O <? 

i * * 3 K 



FIG. 6. Attenuation characteristics of networks of Fig. 4. 

satisfactory, half -filter sections will suffice. An attenuation change 
rate of about 6 db. per octave can be secured by means of the end 
sections alone. 

Fig. 4 shows six types of dividing networks, together with their 
design formulas, three of which are parallel types and the remainder 
the corresponding inverse series type. Networks a and b each contain 



70 J. K. MILLIARD AND H. R. KIMBALL [J. S. M. P. E. 

one and a half filter sections; that is, the half end section and one 
full prototype section. Networks c and d are single-section networks, 
and networks e and / contain only the end sections. The formulas 
given provide means of computing the electrical constants for any cut- 
off frequency, denoted by f c , and any resistive impedance, R . 

In Fig. 5 the values of the electrical constants for the elements of 
the various networks of Fig. 4 have been tabulated for a cut-off 
frequency of f c and a value of R equal to 10 ohms. For networks 
a, b, c, and d, the value of M is taken equal to 0.6; whereas for net- 
works e and /, M was made equal to zero, the reason for which is 
explained later, in the section dealing with impedances. For other 
values of R the values of the coil inductances increase directly with 
increase in the value of R and capacitances decrease with increase 
in the value of R . 

ATTENUATION AND PHASE CHARACTERISTICS 

The attenuation characteristics for the various dividing networks 
of Fig. 4, when operating between resistances of R ohms, are 
shown in Fig. 6. In preparing the curves it was assumed that the 
coils and condensers were non-resistive. In practice, where the com- 
ponent electrical elements contain some resistance, the curves will 
be slightly different, especially in the cross-over region. This, in 
some cases, has the effect of shifting the cross-over point slightly away 
from the theoretical cut-off point. 

The amount of attenuation that the networks exhibit in their 
passing bands is especially important for high-powered sound systems. 
For instance, in a 100-watt system, a loss of 1 db. in the dividing net- 
work means about 25 watts' loss of power. This, it is easy to realize, 
is an important loss, because the final power amplifiers must supply 
this amount of power in addition to what is needed to produce the 
desired sound energy. Where care is taken to make use of low-resis- 
tance coils for the dividing network, this loss can be reduced to 
about 0.5 db. 

In the paper by J. K. Milliard describing the Shearer two-way horn 
system, 4 * it is pointed out that all virtual sources of the reproduced 
sound from a speaker system should coincide in a vertical plane. In 
arriving at the most desirable relative location for the high-range 
and low-range speakers to achieve this effect, it is useful to have 

* See p. 45. 



July, 1936] DIVIDING NETWORKS FOR LOUD SPEAKERS 



71 



available the phase-shift of the dividing networks at the cross-over 
points. These phase shifts are noted in Fig. 6. 



IMPEDANCE CHARACTERISTICS 



The impedances obtained at the input terminals of the dividing 
networks of Fig. 4 vary, of course, from network to network. In 




*k 



\\ 



ess 



RESISTIVE COMPONENT 



KtACTIVE COMPONENT 



FIG. 7. Components of impedance at input terminals of network 
d, Fig. 4: (a) upper, resistive component; (&) lower, reactive 
component. 

general, the impedances of any of the corresponding series and parallel 
types are inverse to each other. This follows from the manner in 
which the series types of network were derived from the parallel 



72 J. K. HlLLIARD AND H. R. KlMBALL [J. S. M. P. E. 

types. In order to obtain image impedance characteristics at the 
input terminals of the networks, it would be necessary to use image 
impedance matching loads at the output terminals, as shown in 
Fig. 1. In practice, where the speakers are arranged in series- 
parallel combinations to give load resistances as closely as possible 
to R ohms at the high- and low-range output terminals, the input 
impedances will not adhere strictly to image impedance character- 
istics. However, for networks a and b, which contain a fair amount 
of masking because of the intervening filter sections, this change 
should not be great in the filter passing bands. 

In connection with networks c and d, which provide less masking, 
it is instructive to view the input impedances obtained for various 
values of M and for speaker load resistances of R ohms. Figs. 7a 
.and 7b give the resistive component and the reactive component, 
respectively, of the input impedance for network d of Fig. 4. It is 
observed that some improvement in the sending-end impedance 
might be obtained by using M = 0.45 instead of M = 0.6. The 
change in the attenuation curve which a design of this nature pro- 
duces, however, is very small, and for this reason design data for 
such a network were not included in Fig. 5. 

In connection with networks e and/, which consist only of the half- 
section terminations, it is necessary to employ a value of M = 0.0. 
This gives a constant input impedance of R ohms for load resistances 
of R ohms. The design formulas given in Fig. 4 for these networks, 
therefore, do not contain the parameter M. 

For the designs of Fig. 4, some have mid-series image impedance 
characteristics at the sets of output terminals, and others are mid- 
shunt terminated. A feature of the mid-series termination is that 
the image impedance in the passing band is a resistance of R ohms 
at frequencies remote from the cut-off and gradually reduces theo- 
retically to zero ohms at the cut-off. The mid-shunt termination, on 
the other hand, is R ohms at points remote from the cut-off and 
gradually increases to infinity at the cut-off. That is, these two 
image impedance characteristics are inverse to each other. Now 
it so happens that low-frequency dynamic speakers have a mechanical 
anti-resonance point at frequencies of 100 or lower. This results in 
low-frequency speakers having a relatively high input impedance at 
the lower frequencies which gradually reduces to the nominal im- 
pedance as the frequency increases. Hence, the writers have achieved 
more uniform over-all attenuation in connection with low-frequency 



July, 1936 J DIVIDING NETWORKS FOR LOUD SPEAKERS 73 

dynamic speakers by using dividing networks having internal mid- 
series image impedances at the low -frequency horn terminals. For 
instance, network d of Fig. 4 in actual operation gave better results 
than network c because of better impedance-matching conditions for 
low-frequency units. 

CONSTRUCTIONAL FEATURES 

The methods employed for assembling and wiring a dividing net- 
work may vary considerably, depending upon system requirements. 
In regard to the filter coils, as already mentioned, it is desirable to 
give considerable thought to theif type and to their effective re- 
sistance. Where iron or some form of steel is used for the coil cores, 
modulation results if the coils are overloaded. Also, if the effective 
resistance is unduly large, excessive loss in the filter bands will result. 
The writers have found that large-size air-core coils solve the problem 
about as effectively as any other method. 

REFERENCES 

1 ZOBEL, O. J.: "Series and Parallel Operation of Wave Filters," U. S. Patent 
1,557,230, Oct. 13, 1925. 

2 SHEA, T. E.: "Transmission Networks and Wave Filters," D. Van Nostrand 
Company, Inc., New York, N. Y. (1929). 

3 JOHNSON, K. S.: "Transmission Circuits for Telephonic Communication," 
D. Van Nostrand Company, Inc., New York, N. Y. (1927). 

4 MILLIARD, J. K.: "A Study of Theater Loud Speakers and the Resultant De- 
velopment of the Shearer Two- Way Horn System," Technical Bulletin, Research 
Council, Acad. Mot. Pict. Arts & Sci., Mar. 2, 1936. (Reprinted, J. Soc. Mot. 
Pict. Eng., XXVH (July, 1936), No. 1, p. 45. 



TELEVISION 

from the Standpoint of the 

MOTION PICTURE PRODUCTION INDUSTRY 

Summary. A report of the Scientific Committee of the Research Council of the 
Academy of Motion Picture Arts and Sciences, Hollywood, California, May 18, 
1936. Whereas excessive skepticism held the minds of those in the industry some 
years ago when sound was about to be introduced into the picture, now, in the case 
of television, instead of disbelief, we have excessive credulity. The report discusses 
briefly a few of the factors that would be involved upon the introduction of television, 
and concludes with the statement that there appears to be no danger that television 
will burst unexpectedly upon an unprepared motion picture industry. 

The present position of sound motion pictures, confronted by the 
developing art of television, differs fundamentally from the situation 
of silent pictures before the advent of sound. Viewed in the perspec- 
tive of ten years, it is clear that before the premiere of Don Juan and 
the accompanying sound picture program at the Warner Theater 
in New York on August 6, 1926, all the elements favoring the transi- 
tion from silent to sound pictures were present. Broadcasting had 
already attained a formidable place in the entertainment world, 
demonstrating that reproduced sound was acceptable to the public. 
The electric phonograph had reached a high degree of development. 
Public address systems had been used in the last Liberty Loan drive 
during the War, at President Harding's inauguration in 1921, and 
subsequently in national political campaigns and other events calling 
for the distribution of sound to large audiences. Electrical inter- 
locks had been applied in industry, and were available for the syn- 
chronization of scene and sound. The technological obstacles had 
been overcome. 

Yet all but a few persons in the picture business were skeptical. 
On the technical side, those who remembered the earlier abortive 
attempts to link sound with pictures ignored the recent advances in 
sound reproduction, although the evidences were before them. Once 
the technical feasibility of sound pictures had been proved, they 
were sure that the public did not want them. Even after the notable 
commercial success of early sound picture productions, this belief 
survived for some years. 
74 



TELEVISION 75 

As a result of such excessive skepticism within the industry, the 
transition from silent to sound pictures was hurried, disorderly, and 
costly. There is no likelihood of a repetition of such a crisis when 
television becomes a commercial factor. Instead of disbelief, we 
have, in the case of television, excessive credulity. Both picture 
people and the public have been waiting for television for five years. 

Besides psychological preparedness, the preventive factors keep- 
ing television from coming unexpectedly upon our industry are the 
great technical and commercial complexity of the new medium, and 
the existence in the picture business of technically trained personnel 
capable of following the progress of television and of giving notice 
of impending developments. 

Television has reached a point in its laboratory development where 
a small picture (about 6 by 8 inches) with moderate entertainment 
value, can be transmitted, but with far more complicated equipment 
than motion picture recording and sound broadcasting require. The 
cost of development up to this point may be measured in millions of 
dollars. Before there is any possibility of nation-wide exploitation, 
hundreds of millions of dollars must be expended for numerous 
transmitting stations of limited range, connecting cables of new de- 
sign and receivers. None of these things can be attained overnight. 
There is a possibility that such a development may start in 1937, or 
more probably in 1938. It should be noted that its scope, as far as 
we can prevision it, is limited to home entertainment purposes in 
urban areas. 

Barring revolutionary inventions, there is as yet no promise of the 
enlargement of the field of television to theater screen size, nor of an 
extension of the possible service area to rural districts in this country. 

In the United States a start is being made in reducing television to 
practice in the field. A new transmitting station is being installed 
in the tower of the Empire State Building for an experimental service 
in the City of New York, to begin this fall. About 150 receivers will 
be furnished to selected observers. These receivers are being manu- 
factured at a cost of probably several thousands of dollars apiece, 
and even upon a quantity production basis it is difficult to see how the 
cost of the present design could be reduced below three hundred 
dollars. 

A new type of cable, suitable for the transmission of television 
images, is being installed for tests and possible subsequent commer- 
cial use between Philadelphia and New York City. Similar develop- 



76 TELEVISION 

ments are in progress in England, Germany, France, and other coun- 
tries. In 1937, therefore, considerable data should be available on 
points that are now obscure. 

This Committee has been making a study of the technical progress 
of television during the past year, and possesses a general knowledge 
of the principal systems under development. A bibliography of the 
available literature has been compiled and is being kept up to date. 

We shall endeavor to keep in touch with the pioneering attempts to 
make television a commercial reality, and as progress occurs reports 
will be made from time to time. Other than this no action by the 
Research Council of the Academy appears to be called for during the 
balance of 1936. 

There appears to be no danger that television will burst un- 
expectedly upon an unprepared motion picture industry. 

SCIENTIFIC COMMITTEE, RESEARCH COUNCIL 

CARL DREHER, Chairman 

GORDON CHAMBERS N. M. LAPORTE GORDON S. MITCHELL 

L. E. CLARK WESLEY C. MILLER HOLLIS MOYSE 

J. G. FRAYNE WILLIAM MUELLER 



ACTIVITIES OF SCIENCE SERVICE IN SCIENTIFIC 
DOCUMENTATION* 



WATSON DAVIS** 

Summary. As an aid to scientific research, Science Service has sponsored de- 
velopment and operation of microphotographic duplication, making available copies 
of books in libraries and science documents in two forms: (1) reduced-size photo- 
graphic images upon standard 35-mm. motion picture film, called microfilms; (2} 
photoprint enlargements from the microfilms. Microfilms need optical aid in order 
to be read, whereas photoprints can be read with the unaided eye. Two services are in 
active operation: namely, the Bibliofilm Service in the Library of the U. S. Depart- 
ment of Agriculture, and the Auxiliary Publication Service in cooperation with 
editors of scientific journals. Application of microphoto graphic duplication to the 
important and complex problem of bibliography is suggested. 

The dissemination of science is of importance equal to the conduct 
of research. If discoveries and inquiries in the physical and natural 
sciences are not made known to the scientific world and the public 
so that they may be utilized and applied, the new knowledge might 
just as well not have been created. 

The first step in dissemination is publication in some manner of 
the research results. The second step is the incorporation of refer- 
ences to published research results into usable bibliography. These 
two steps constitute the mechanism of science dissemination to the 
scientific world. 

Realizing the importance of scientific documentation in a very 
broad sense, Science Service has been interested for the past decade 
in the problems of scientific publication and bibliography, urging 
particularly exploration of the possibilities of microphotographic 
duplication, i. e., reduced-size photographic images of documents 
upon film or paper. 

In 1926 Dr. Edwin E. Slosson, late director of Science Service, 
and the author, urged in correspondence, conference, and by memo- 
randa that attention be given to the use of microphotographic duplica- 



* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** Science Service, Washington, D. C. 



77 



78 W. DAVIS |j. s. M. p. E. 

tion in scientific publication. Under date of August 19, 1933, the 
author issued for purposes of discussion and criticism a mimeographed 
memorandum, Project for Scientific Publication and Bibliography, 
which discussed methods of publication and bibliography, and sug- 
gested the advantages of microphotographic duplication and mecha- 
nization of bibliographic methods. 

Conferences under the auspices of Science Service were held to dis- 
cuss the proposals. Discussion and experimentation by individuals 
and institutions had progressed to the point in 1935 where it seemed 
advisable to contemplate inaugurating some of the phases of the 
project. Mr. Francis P. Garvan made available in July, 1935, a 
Chemical Foundation grant of fifteen thousand dollars for initial 
exploration, development of mechanisms, and inauguration of some 
phases of the publication project. There was therefore organized the 
Documentation Division of Science Service. 

There has been considerable independent interest, principally upon 
the part of librarians and scholars working in the fields of the humani- 
ties and history, in the possibilities of applying microphotographic 
duplication to their problems. Several libraries have put into use 
for research purposes microphotographic duplication upon 35-mm. 
film. Microphotographic duplication as a means of copying and re- 
cording has been advocated and utilized in other instances. Some 
cameras and other apparatus for the purpose have become available 
commercially in America and in Europe. 

Science Service is devoting the energies and resources of its Docu- 
mentation Division to : 

(a) Development of mechanisms useful in microphotographic and other photo- 
graphic duplication and in bibliography. 

(b) Publication of scientific papers and monographs that can not now win 
prompt or complete issuance. 

(c) Cooperation with libraries in making available by photographic methods 
the literature of the past. (Bibliofilm Service, operated by Science Service in the 
Library of the U. S. Department of Agriculture.) 

(d) Investigation of the broad problem of scientific bibliography and useful 
mechanisms. 

MECHANISMS 

It is necessary to develop camera, projection printer, reading 
machine, and other mechanisms of adequate design to carry out the 
photographic copying and publishing procedures contemplated and 
to allow the reading of microphotographic films. Science Service is 



July, 1936] SCIENTIFIC DOCUMENTATION 79 

fortunate in having the cooperation of the U. S. Naval Medical School, 
the U. S. Department of Agriculture, and the U. S. Bureau of the 
Census in this development. Dr. R. H. Draeger, MC, USN, is in 
charge of the development of mechanisms. Dr. Draeger's original 
35-mm. microphotographic camera is the one being used by the 
Bibliofilm Service in the U. S. Department of Agriculture Library. 
The mechanisms consist of: 

(1) Cameras for copying typescripts, books, photographs, etc., 
upon 35-mm. film.* (In use and under design.) 

(2) Supplementary apparatus for camera such as book-holder 
for camera,* film container, etc. (Models completed.) 

(3) Reading machine : About the size of a typewriter, producing 
large-sized, easily readable images of 35-mm. microfilms. (Model 
completed.) 

(4) Microfilm viewer: A small monocular optical device for 
reading 35-mm. microfilms a line at a time, suitable for inspecting 
film or for use while travelling. Will sell for about a dollar. (Design 
completed.) 

(5) Projection printer: Automatic device for producing photo- 
copies (enlargements upon paper) from 35-mm. microfilm negatives.* 
(Under design.) 

(6) Developing and processing apparatus for 35-mm. microfilm 
and paper projection prints.* (In use and under design.) 

SCIENTIFIC PUBLICATION 

Scientific publication is accomplished primarily through scientific 
journals. The continuance of prompt, full, and economically justi- 
fiable publication is essential to scientific progress. The advance of 
science has brought about a multiplication of journals and increasing 
difficulty in maintaining their support and distribution. 

In increasingly frequent instances it is impossible to arrange for 
prompt and complete publication of research results because of the 
cost of publication under the present methods. Journals find it 
necessary to limit the length of papers published and to reject papers 
that would have only a limited audience. After publication, it is 
often difficult to obtain a copy of a journal containing a desired paper, 

* Primarily intended for use in microphotographic laboratories. Arrangements 
are being made for the production of these mechanisms separately or as complete 
microphotographic laboratories, so that libraries and other institutions can be 
supplied. 



80 W. DAVIS [j. s. M. p. E. 

because of (a) the limited number of copies printed, (b) inadequate 
distribution of journals to libraries, and (c) the fact that a journal is 
usually "out-of-print" immediately after issuance. 

For the publication of those scientific papers and monographs that 
can not now win prompt or complete publication, Science Service 
is offering cooperation with existing journals and societies in the 
following plan : 

(7) Editors of scientific journals submit to Science Service those 
manuscripts that they find it impossible to publish promptly or 
completely. 

(2) Editors would publish in their journals a notice, giving title, 
author, abstract, serial document number, and price, informing 
readers that the complete paper photographically reproduced is 
obtainable from Science Service. 

(3) The manuscript is typed by the author upon 8 1 /* X 11 -inch 
(letter-size) paper in a standard manner for photographic publication. 

(4) Pages of typescript would then be photographed upon 35-mm. 
film, which would be the master negative. 

(5) When an order for a paper is received, its film negative is 
used to make a positive for distribution. The positives would be 
available in two forms: (a) Paper photographic prints made by 
projection, suitable for direct reading without optical aid. These 
would be approximately 6X8 inches, or seven-tenths the original 
typescript; (b) film positives, contact prints on film, for use in read- 
ing machines. 

(6) A person desiring a copy of the paper or monograph would 
learn of its availability through the abstract published by the scientific 
journal thus relieved of the necessity of printing it. He would order 
by number, remitting the cost at the time of ordering. Each order 
would be filled promptly by making a photographic copy in the form 
desired from the master negative. Each copy would be made to 
order, thus obviating the necessity of keeping copies in stock, which, 
in the case of printed publications, requires large filing or storage 
space. Master negatives compactly stored as 35-mm. film upon reels, 
like motion picture films, would be perpetually available, and a 
paper or monograph would therefore never be "out-of-print." 

(7) The cost of copies of papers would be reasonable : projection 
prints, 5 cents per page; microfilm, 1 cent per page. 1 



July, 1936] SCIENTIFIC DOCUMENTATION 81 

MAKING AVAILABLE EXISTING LITERATURE 

Another problem confronting the scientific world is that of making 
available the existing literature. Only workers with access to large 
libraries are served with any approach to adequacy by the existing 
methods and resources of libraries. Even under the most ideal condi- 
tions the loan of a journal, periodical, or book to one reader makes 
it inaccessible to another. 

Libraries have in some instances used microphotographic duplica- 
tion upon 35-mm. film for making their material available, particu- 
larly manuscripts and rare books, to scholars and research workers. 

The practicability of substituting microphotographic copying on 
35-mm. film for inter-library loans has been demonstrated by the 
establishment of the Bibliofilm Service operated by Science Service 
in the U. S. Department of Agriculture Library. 

The question of property right or copyright is also one that arises 
in connection with photocopying in libraries. This is not likely to 
be so important in the fields of physical and natural science as in 
the fields of social, historical, and economic science. Inquiries and 
arrangements of a practical nature have been inaugurated upon this 
problem. (Agreement between Joint Committee on Materials for 
Research and National Association of Book Publishers, May, 1935.) 

TABLES OF CONTENTS AND INDEXES 

As a possible useful service capable of being rendered by micro- 
photographic duplication when reading machines are available, it 
has been suggested that the tables of contents of current journals 
could be made available at weekly or monthly intervals. It is be- 
lieved that this service would call the attention of many libraries 
and research workers to the usefulness of many journals they do not 
now read, and that it would stimulate the distribution of the journals. 

With the cooperation of societies and publishers, tables of contents 
and indexes of past volumes of scientific journals might be furnished 
as microfilms. 

PUBLICATION OF SCIENTIFIC JOURNALS 

As a possibility for the future, upon which experiments are being 
conducted, there is the publication of journals by microphotography. 
Placing a photographic image of an S l /z X 11 -inch letter-size type- 
script upon an area x /4 inch or less in height is believed to be a tech- 
nical possibility. A piece of film the size of a library catalog card, 



82 W. DAVIS [J. S. M. P. E. 

3X5 inches, would then carry 150 to 200 pages of typescript, the 
equivalent of the ordinary issue of a sizable scientific journal. With 
the development of a suitable reading machine for these microphoto- 
graphs, it would be possible to provide at a reasonable yearly sub- 
scription such a reading machine to a subscriber on a rental or time- 
payment basis together with the monthly issues of film carrying the 
images of the material being published. 2 

SCIENTIFIC BIBLIOGRAPHY 

Scientific bibliography is in an unfortunately chaotic state at the 
present time. Some of the most important efforts toward bibliog- 
raphy have been suspended or are endangered (International Cata- 
log of Scientific Literature; Biological Abstracts, etc.). 

Bibliography must be essentially a personal service. It can hardly 
be expected that each scientific worker, or even each library, will 
have in stock all the bibliography needed upon any subject. There 
can be assembled in one or two places, serving the whole world, a 
complete scientific bibliography instantly available to provide "to- 
order" service. Cost of the proposed adequate system of biblio- 
graphy will be far less than the present ineffective scattered efforts. 

With the purpose of making available without library research 
any sort of references to scientific literature and bibliographies upon 
particular research subjects, there would be instituted and operated 
a bibliographical file and production service which would ideally 
absorb existing bibliographical schemes in all fields of science and 
provide bibliographical material in those fields of science that are 
now not easily accessible. The Documentation Division of Science 
Service is investigating and studying this matter. 

For every published article, past and current, there would be as 
many abstract bibliography entries in a bibliographical file as there 
are subject classifications under which the article should be indexed. 
The "file" might be a roll of 35-mm. film. A complete and compre- 
hensive scheme of numerical classification by subject would be created 
by utilizing existing subject classifications in science, so far as they 
can be utilized (International Dewey Classification?), and the crea- 
tion of new subject classification schemes for unclassified areas of 
science. Upon each card (the word "card" is used, although the item 
in the bibliographical index might not be of paper material) would 
appear the abstract bibliographical entry and also a subject classifica- 
tion pictured or otherwise marked so as to actuate a selecting mech- 



July, 1936] SCIENTIFIC DOCUMENTATION 83 

anism, the "eye" of which would probably be a photoelectric cell. 
Once these bibliographical compilations are made, this selector would 
pick the classifications desired. The selector would be linked mechani- 
cally to the microphotographic camera. In this way it would be 
possible to receive a request from a scientist for a bibliography upon 
a certain subject and supply it by setting the selectors to select the 
number corresponding to that subject classification, the camera 
wedded to the selector producing, to order, the bibliography desired. 

By using photographic methods it would be practicable photo- 
graphically to transfer to the bibliographical index these entries from 
past and existing bibliographies. Existing bibliographical efforts could 
be coordinated or absorbed to provide current and continuing bibliog- 
raphies. 

The bibliography thus produced would be sent to the scientist 
in a microphotographic form, or, at higher cost, the microphotographs 
could be used to produce photographic projection prints capable of 
being read with the unaided eye. 

While the inauguration of the publication projects can be accom- 
plished in a matter of months, the possible inauguration of a biblio- 
graphical project is a matter of years and considerable expenditure 
of money. Careful exploration of the bibliographical project is 
indicated. 

REFERENCES 

1 Documents 152, 153, Science Service, Washington, D. C. 

2 Document 46, ibid. 



SOME TECHNICAL ASPECTS OF MICROPHOTOGRAPHY 5 

R. H. DRAEGER** 



Summary. Photographs are shown of a book-copying camera using 35-mm, posi- 
tive motion picture film, and the special features of this camera are discussed. The 
problem of the reduction ratio is discussed and illustrations shown, with the conclu- 
sion that a 10 or 12 to 1 reduction ratio should be employed for book copy work on 
35-mm. positive motion picture film. 

Photographs are shown of a reading machine of the author's design, and various 
aspects of the problem are discussed. 



The rapid increase in scientific research during this century has 
brought about an enormous volume of data for yearly publication, 
the financial burden of which is now weighing heavily upon the exist- 
ing scientific journals. This condition makes it desirable to find some 
less voluminous and less expensive method of documentation. 

Microphotography offers a possible solution of the problem. 
Although proposed and its advantages recognized during the nine- 
teenth century, very little use has been made of it, due to the various 
technical difficulties that beset the art. 

The excellent progress in preparing fine-grained emulsions makes it 
possible to copy printed matter in reduced form, duplicating it 
photographically to a degree of perfection depending upon the 
quality of the apparatus used and the reduction ratio employed. 

In 1932 the author undertook the design and construction of a 
camera suitable for copying the printed pages of books on positive 
motion picture film. The camera was completed in 1934, and at the 
present time is being used to operate the Biblio -service of the Library 
of the U. S. Department of Agriculture. A newly designed camera 
is nearing completion at the Navy Medical School, a model of which 
is also being constructed for the Library of Congress. This camera 
has a film capacity of 1000 feet, automatic focusing, and automatic 
timing. Completely automatic action has been provided for copying 

* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** Lieutenant, Medical Corps, U. S. N. 
84 



TECHNICAL ASPECTS OF MICROPHOTOGRAPHY 85 

loose sheets or cards which may be readily fed beneath the camera. 
Provision has been made to use either 35- or 16-mm. film, and in the 
case of the model for the Library of Congress 70-mm. film may also 
be used. 

Fig. 1 is a view of the original camera, mentioned above, and shows 
the principal features that have been incorporated into its design. 
The apparatus consists of a table, a supporting rod, a camera support 
arm, the camera, a book holder, and lighting, indexing, and timing 




FIG. 1. Original book-copying camera. 

mechanisms. The camera proper hangs vertically downward, its lens 
pointing toward the book below. 

The book is placed upon a special support which automatically 
centers it and keeps it in the proper position against a counterbalanced 
hinged glass plate which rises automatically at the end of each exposure. 
The glass plate is in the focal plane of the lens when in a horizontal 
position and maintains the book pages in proper focus. The two open 
pages of the book are photographed simultaneously and appear upon 
the film as shown in Fig. 2. 

The lights consist of two banks of lamps which are turned on and 
off with each exposure. The indexing of the film and timing of the 
exposure are accomplished automatically. The lens used is a Zeiss 



86 



R. H. DRAEGER 



fj. S. M. P. E. 



Tessar //6.3, 3V 2 -inch focal length. The magazine capacity is 150 
feet of 35-mm. motion picture film. Positive film is used, because it 
has good contrast, fine grain, and is considerably cheaper than the 
negative stock. 

The operation of the camera is simple. The operator places the 
book upon the book holder and adjusts the platens to the proper 
height to accommodate the thickness of the particular book. He then 
measures the height of the book pages in inches and sets the camera 
support arm at the proper height and the lens spiral for the proper 
focus. The scales for these two settings are marked to correspond 
with the book height in inches so as to produce an accurately focused 
image completely filling the frame of film to be exposed. 

The hinged glass cover is then pulled down to a horizontal position 




FIG. 2. 



Strip of motion picture film having a book-page 
image on each 3 / 4 X 1-inch frame. 



over the first pages to be copied. This closes a contact which turns on 
the lights and opens the lens shutter. At the termination of the 
exposure, the lights go out, the shutter closes, and the hinged glass 
book cover is tripped and returned to the raised position. The 
operator turns to the next page to be copied, and repeats the pro- 
cedure for as many pages as are to be copied. Since two open pages 
of a book are copied simultaneously, a speed of 1000 pages per 
hour is easily attained. 

Figs. 3 and 4 are views of the reading machine, which is of the trans- 
luscent screen variety. The screen is arranged at a comfortable read- 
ing angle before the reader. The lamp house and indexing mechanism 
are carried upon a rotatable head above the screen. Turning from 
page to page is accomplished by the simple movement of either small 
hand-crank on the head. The film is loaded into the machine without 
any threading operation. 



July, 1936] TECHNICAL ASPECTS OF MICROPHOTOGRAPHY 



87 



The film gate consists of two parallel plates of glass, one stationary 
and one hinged. The hinged plate is so arranged that it opens before 
the film is moved in either direction so that the film moves only 
through an open slot. The arrangement mentioned above has been 
found to be the only satisfactory method of holding the film in a plane 
for critical projection. A film gate consisting of an aperture plate 
allows slight bending of the film and consequent loss of detail in the 
projected image. A special feature of the device is its rotatable head, 





FIG. 3. Reading machine, 
translucent screen variety. 



FIG. 4. Reading machine, show- 
ing 90-degree rotation of the head. 



which enables images placed upon the film in any orientation to be 
read. 

Let us now consider other problems in connection with microcopy- 
ing. The reduction ratio employed depends upon the resolving power 
of the film and the use to which the copy is to be put. If the copy 
is for record purposes and to be filed for occasional use only, a higher 
reduction ratio is justified. If the material copied upon the film is 
primarily intended for reading or reproduction, the reduction ratio 
should be such that the original and copy will have similar appear- 
ances when the copy is enlarged to the size of the original. This is 
necessary if ease of reading is to be enjoyed and eye-strain avoided. 



88 



R. H. DRAEGER 



|J. S. M. P. E. 



The reduction ratio which will afford this result is a controversial 
point. Obviously, the greater the reduction ratio the less the cost 
and the greater the saving in storage space. However, this is not the 
only consideration, and should not be allowed to overbalance the issue. 
In order to test the resolving power of the film used in the above- 
described camera, a test screen (Fig. 5) was made and uniformly 
illuminated. The screen was originally drawn to a large scale, and 
then reduced photographically to approximately 20 millimeters 
square on a lantern-slide plate. The lines on the lantern-slide screen 
were separated by a distance in microns equal to ten times the 
number shown to the right of each of the eight squares. Thus when 




FIG. 5. Apparatus for testing resolving power of 
film for micro-copying camera. 

the screen is photographed upon the motion picture film at a reduction 
of 10 diamejters, the numbers designate the microns of separation of 
the corresponding lines. By making exposures with this device in 
various positions, images were placed at several points over the film 
gate area. 

The film was then processed and studied under the low-power 
microscope, whereupon it was easily ascertained which of the lines 
were resolved. Using an elon-hydroquinone developer, the 25-micron 
lines were readily resolved over the entire film aperture. By using 
special precautions, fine-grain development, and employing the cen- 
ter of the field only, the 15-micron lines were discernible. 

This apparatus has proved to be useful in checking not only the 
resolution of the film, but the focus of the lens and the effect of the 
lens apertures, and the definition of the lens may likewise be de- 



July, 1936] TECHNICAL ASPECTS OF MICROPHOTOGRAPHY 



89 



termined by having one factor variable and keeping the other con- 
stant. The depth of focus may be easily determined by making a 
series of exposures at slightly increased and decreased distances from 
the focal point of the lens. 

Fig. 6 is a photomicrograph of a few letters from a film copy of a 
printed page made at a reduction 
ratio of 10 diameters. It will be 
seen that the silver grains are 
readily seen but that the letters are 
also clearly legible. At higher re- 
duction ratios the graininess of the 
film becomes more apparent. 

At a reduction ratio of 10, photo- 
print reproductions may be made 
from films that resemble the original 
very closely. As finer-grained 
emulsions are developed, higher 
reduction ratios may be employed. 
However, if satisfactory results are 
to be attained, the reduction ratio 




FIG. 6. Photomicrograph of film 
copy of printed page (x 10). 



should not exceed a definite relation to the resolving power of the 
film. 

It is hoped that this important point will be kept in mind by those 
engaged in microphotographic work in order that the public apprecia- 
tion of this new and promising field may not be stifled by imposing 
too great a hardship upon the reader. 



MICROFILM COPYING OF DOCUMENTS* 
T. R. SCHELLENBERG** 



Summary. Microphotographic duplication peculiarly fits the research needs of 
modern scholarship for the following reasons: it reduces the bulk of records in the 
same geometric ratio in which they are accumulating; it makes them as permanent 
as they are now ephemeral; it makes them mobile, permitting a more widespread use of 
them; it makes it possible to supply records for specialized use; it facilitates the co- 
operative exploitation of records that have become so extensive that they can no longer 
be mastered individually; and it permits a more exact and accurate use of records. 



During the Franco-Prussian war, a photographer within the 
beleaguered city of Paris developed a means of copying messages 
upon film to be transmitted by carrier pigeons to anxious compatriots 
in the provinces. About 115,000 such dispatches were sent to and 
from the city during the siege. After the war the process of making 
microfilm copies of documents was described in a pamphlet, in which 
was inserted a specimen of the rolls of film that had been produced. 
Sixty-four years later this film was discovered by Dr. Bendikson in 
the rare collections of the Huntington Library. Dr. Bendikson made 
an enlarged print of the film, which he reproduced in the February, 
1935, issue of The Library Journal. The document, which had been 
copied at a reduction of 32 diameters, was quite legible after the lapse 
of more than half a century. 

Little progress was made in copying documents upon film until 
another great emergency. During the World War, German military 
authorities made extensive use of photographic equipment for copying 
military secrets. A German scholar, following in the wake of the 
Austrian armies, also made use of the process for copying historical 
documents. In the Minerva-Zeitschrift for 1930 he describes how, 
over night in a dingy room of a monastery in the Albanian mountains, 

* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** Executive Secretary, Joint Committee on Materials for Research, of the 
American Council of Learned Societies and the Social Science Research Council, 
The National Archives, Washington, D. C. 
90 



MICROFILM COPYING OF DOCUMENTS 91 

he made copies by means of a Leica camera of a whole body of valu- 
able papers that were destroyed soon thereafter. 

Just as micro-copying peculiarly met the needs for the reproduction 
of documents in the special emergencies that I have just indicated, so 
microphotographic duplication will fulfill the research needs of 
present-day scholarship. There are several reasons why this is the 
case. By microphotographic technic I simply mean making a film 
copy of a document, which is to be read not by making enlarged prints 
from it, but by throwing the image of the film by means of a projector 
or reading device upon a surface from which it is to be read. 

The first reason is this: micro-copying offers a means of reducing 
the bulk of documents in the same geometric ratio in which their 
bulk has been increased. With the complexity of our life has come a 
proportionate increase in the quantity of records pertaining to its 
activities. So great is the increase that the depositories of such rec- 
ords are faced with the prospect of doubling their capacity every dec- 
ade. By resorting to micro-copying, however, the ever-increasing 
accumulation of modern materials, which threatens to stultify our 
present research methods, can be brought under control. By photo- 
graphing at a reduction of 16 diameters, newspapers, for example, 
are being reduced by means of the Recordak machine developed by the 
Eastman Kodak Company, to a surface occupying 1 / 2 B6 the original 
area. It is likely, then, that bulky materials like newspapers, large 
series of schedules like those accumulated by the Census Bureau and 
other units of government, transcripts of hearings like those held before 
the NRA and AAA, in fact, any large rational series of documents, 
which has no intrinsic historical interest but which should be preserved 
for the information it contains, may, in the future, be copied upon 
film for the conservation of storage space. The great mass of records 
that constitute the evidences of the New Deal may have to be filmed 
so that it is possible to administer them. The point is soon reached 
when it becomes cheaper to film the documents than to provide 
storage space for them. 

Just as the quantity of records has increased in geometric pro- 
portions, so the records have become constantly more ephemeral in 
character, both because of the quality of their content and because 
of the quality of the material upon which they have been produced. 
This fact makes apparent the second reason why microfilm copying 
is peculiarly suited to fulfill modern research needs. While the 
permanency of films is still an open question, which fortunately 



92 T. R. SCHELLENBERG [J. S. M. P. E. 

will be answered as a result of the study of film stability being made 
by the National Bureau of Standards, there is no doubt that filming 
is the only possible means of preserving many of the newspapers 
issued on wood-pulp paper and many of the government serials 
issued by the Latin- American and European countries. Further- 
more, in business and governmental work there are being created 
great masses of documents that serve only temporary purposes, 
but which throw very great light upon the operation of both business 
and government. Such material constitutes the raw-stuff for re- 
search in the social sciences. It is material that is so unorganized 
that it is not fit for publication in its present form, but also is so 
rich in informational content that it should not be destroyed. Among 
such records, for example, are the foreign cable dispatches of news 
agencies like the United Press and the Associated Press, ordinarily 
kept for two years, after which the statute of limitations removes the 
danger of libel suits. Such records can be preserved cheaply in film 
form, though the preservation of the originals would be an impossi- 
bility. 

The third reason why microfilm copying peculiarly meets the needs 
of modern scholarship is that it renders research materials mobile. 
It was for this very reason that documents were filmed during the 
Franco-Prussian War and the World War. The films could be carried 
by the wings of carrier pigeons. It is conceivable that the cost of 
producing microfilm copies of documents will be brought to so low 
a level that it will be less than the cost of mailing the original as an 
inter-library loan. The most conspicuous attempt to replace inter- 
library loans with film copies is that made by the Department of 
Agriculture library. When large depositories have the equipment 
for producing, and small depositories the equipment for reading 
film copies, the library resources of the country will become fluid. 
Effective research will be possible in small research institutions 
throughout the country, and scholarship will become far more demo- 
cratic in its workings. 

Not only will the introduction of microphotographic technic ren- 
der the existing research materials more accessible, but it will also 
permit the reproduction of highly specialized materials for the 
specialist. This is the fourth reason why film copying meets the needs 
of present-day scholarship. It arises from the fact that micro- 
copying is the only economical method of reproducing documents in 
which minimal unit-costs can be achieved in very small editions. 



July, 1936] MICROFILM COPYING OF DOCUMENTS 93 

This practically brings a return to the conditions subsisting prior 
to the time when Gutenberg developed printing from movable 
type, when it cost no more for scribes to make unique copies 
of a book than to make many copies. Material for which there 
is a demand by only a few scholars might just as readily be 
made available in the form of micro-copies as material demanded by 
the many. 

A fifth reason for the inevitable acceptance of microfilm copying 
is that it facilitates the cooperative exploitation of research materials. 
The records pertaining to social movements have become so extensive 
that they can no longer be mastered individually. In the biblio- 
graphical field, for example, there have arisen innumerable specialized 
bibliographies, so great in number that the use of them is almost as 
difficult as the use of the original references without bibliographical 
aids. Certainly research would be facilitated if, instead, master card 
bibliographies were complied through cooperative effort, of which 
periodically film copies could be made to be distributed among 
research institutions. Likewise, microfilm copying can be utilized 
to advantage in compiling union and regional lists of library hold- 
ings or in compiling a union list of historical manuscripts in this 
country. 

A sixth reason for the use of microfilm copying in research is that 
it permits more exact work. A scholar using a camera like that de- 
veloped by the Folmer-Graflex Corporation can copy manuscript 
and reference materials more extensively and quickly, allowing 
him to make more accurate quotations and citations, more pro- 
longed study, and more exact collations of the records on a given 
subject. 

The wide application of micro-copying to the research problems 
of modern scholarship is an inevitable development. It reduces the 
bulk of records in the same geometric ratio in which they are accumu- 
lating; it makes them as permanent as they are now ephemeral; 
it makes them mobile, permitting a more wide-spread use of them; 
it makes it possible to supply records for specialized use; it facilitates 
cooperative exploitation of records that have become so extensive 
that they can no longer be mastered individually; and it permits a 
more exact and accurate use of records. As the wells of financial 
support for learned institutions run dry, a technic will be employed 
that will make possible the accomplishment of the present objectives 
of scholarship with the expenditure of less money. 



94 T. R. SCHELLENBERG [J. S. M. P. E. 

DISCUSSION 

MR. BRADLEY: I think a word of explanation is due the Society this morning. 
I suggested that this subject be brought up for your consideration largely as a 
matter of disposing of it. It has been pointed out this morning that there may be 
a parting of the ways on sizes, dimensions, and technic in this activity from the 
activities of motion pictures. Frankly, the source of material is about the only 
thing I see now that we have in common. That it will become a new and major 
industry there is no doubt in my mind. 

Mr. Schellenberg and the others have cited source material of a magnitude that 
is almost staggering. I want to cite one other instance, in connection with the 
National Archives, which I have the honor to represent. In 1930, a committee 
was appointed to make a survey of the mass of documents and records in the pos- 
session of the Federal Government and the rate at which it was accumulating. 
At that time it was accumulating at the rate of 200,000 cubic feet annually. 
Under the present administration with our new bureaus and additional functions 
of government, the rate of increase must be considerably higher. What it is I 
do not know. 

There is a committee of Congress called the Committee on Disposal of Execu- 
tive Papers, but altogether there are some fourteen laws governing the disposal 
of various Government papers. There is considerable variation and often con- 
fusion in the routine of such disposition. For example, last year, if I remember 
the figures correctly, the Treasury disposed of ninety-seven tons of papers as 
waste. Sometimes it is burned, sometimes sold as waste, sometimes it is so 
mutilated that it can not be read or used commercially. 

It is thought that if the Bureau of Standards reports favorably upon the life of 
microfilm, The National Archives might reproduce (as a policy of recording) this 
great mass of material into the microfilm form so that the evidence of the originals 
would be preserved even though the physical body should be disposed of. A wild 
guess indicates that we alone might copy some 5,000,000 items annually, or half a 
million feet if we use the motion picture film. But whether or not this is a prob- 
lem for the Society of Motion Picture Engineers, I do not know. Not only 
standard simplified practice, not only a study of film, but a study in nomenclature 
seems to be quite appropriate. 

MR. MITCHELL: It may be of interest to mention the fact that the University 
of Chicago has finished photographing papers dealing with the NRA hearings. I 
do not know the exact figures, but if I recollect correctly, the original would be 
about 1000 volumes of 500 pages each, so you can appreciate the magnitude of 
that one particular task. 

MR. FAMULENER: Have any particular methods of processing been developed 
with a view to minimizing the grain and increasing the reduction ratio that may 
be used? 

MR. BRADLEY: There is a study on foot; in fact there are several studies, and 
the Carnegie Foundation and the National Research Council have made studies 
on the preservation of film. The advisory committee created by the National 
Research Council is acting as a proponent committee on simplified practice in 
which the ratio of reduction will be studied among other things. 

MR. CRABTREE : There has perhaps been a tendency in our Society to overstress 
sound in the past and underestimate the importance of the picture. This par- 



July, 1936] MICROFILM COPYING OF DOCUMENTS 95 

ticular work consists in making pictures on motion picture film, although the re- 
sult attained is certainly not a moving picture. However, I do not see why the 
subject is not cognate to our interests. 

With regard to the question of whether 16- or 35-mm. or wider film will be ade- 
quate, I should say that with expected improvements in emulsions and methods of 
producing fine-grained images, it will probably not be necessary to go to film 
larger than 35-mm. 

MR. TASKER: It might also be interesting to add that the very requirement of 
finer grain, which seems so desirable for this purpose, is equally desirable for the 
motion picture art, and hence developments in the one field are apt to aid those 
in the other. 



NEW MOTION PICTURE APPARATUS 

During the Conventions of the Society, symposiums on new motion picture apparatus 
are held, in which various manufacturers of equipment describe and demonstrate their 
new products and developments. Some of this equipment is described in the follow- 
ing pages; the remainder will be published in subsequent issues of the Journal. 

NEW BACKGROUND PROJECTOR FOR PROCESS CINEMATOGRAPHY* 

H. GRIFFIN** 



A new type of background projector for use in process photography in motion 
picture production studios has been developed which has already been installed in 
studios in England, Sweden, Japan, and the United States (Figs. 1 and 2). 

In appearance this equipment is quite similar to the well known Super Simplex 
projector, but the mechanism, magazines, and lamp house are mounted upon a 
specially built, rigid pedestal assembly in order to eliminate the possibility of 
vibration during operation (Fig. 3). The complete unit is composed of a 
specially constructed Super Simplex mechanism, the usual upper and lower maga- 
zines, and a Hall & Connolly super-high-intensity lamp and lamp house, all 
mounted upon the above-mentioned pedestal. The projector mechanism is built 
especially for the work it must do, and commercial tolerances acceptable for 
theater projection are eliminated in the construction of the process projector. 
The film-trap, for instance, is very accurately constructed, and is equipped with 
edge-guiding means hi order that the picture may be absolutely steady laterally, 
and provision is made in the film-trap design and construction for judging the pro- 
jected picture to determine what causes any unsteadiness that might be present. 

For example, with this equipment it is possible to project a sprocket hole in the 
film, and if the perforations in the film are accurate and they usually are the 
image of the sprocket hole upon the screen is absolutely steady, both laterally and 
vertically. If the negative is projected and the camera frame line moves with 
relation to the perforation, that is a definite indication that the camera movement 
is not steady. If the positive is projected and the positive frame line moves with 
relation to the sprocket holes, that is a definite indication that the camera or the 
printer was unsteady, so that it is possible to observe and analyze satisfactorily 
any defect that may be present in the master print for process projection and thus 
eliminate endless discussion as to where the fault resides. 

The intermittent movement of this particular equipment is of the Geneva type. 
It is manufactured to practically zero tolerance, and steadiness of the movement 
is carefully checked with a special test-film. 



* Presented at the Spring, 1935, Meeting at Hollywood, Calif. 
** International Projector Corp., New York, N. Y. 



96 



NEW MOTION PICTURE APPARATUS 



97 




W) 

c 

'3 



PQ 




98 



NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 



The mechanism may be easily lubricated without opening any of the mechanism 
doors. The bearings are fed through oil-tubes reached from the top of the mecha- 
nism with the exception of the bearing for the intermittent movement, the oil-tube 
for which may be seen through a hole in the door on the non-operating side of the 
mechanism at a certain position of the framing device. 

The lower section of the upper door on the non-operating side of the mechanism 
has been removed, thus making it possible to remove the door after removing the 
hinge screws. Thus it is possible to get into the non-operating side of the mecha- 
nism should it become necessary to do so. The lower door section may be removed 
in the same manner. A grease cup is provided for lubricating the rear shutter 




FIG. 3. Background projector; pedestal assembly. 



shaft, a single turn of which suffices to force sufficient lubrication into the ball 
bearing. A special lubricant has been developed for this purpose. 

No motors are supplied as part of the equipment, for the reason that various 
types of motors are used throughout the world for interlocking systems. A kind 
of motor used on the customer's particular type of interlocking system is furnished 
to the projector manufacturer, and a special motor table is then designed and 
built and rigidly attached to the projector stand in such a position that the motor 
shaft is coupled directly to the drive shaft of the intermittent movement. Lost 
motion is therefore eliminated between the camera shutter and the projector 
shutter, since no gear train is involved in this form of design. 



July, 1936] NEW MOTION PICTURE APPARATUS 99 

The intermittent movement of the projector, as is the case with the camera, 
when properly interlocked operates at 1440 frames per minute standard photo- 
graphing and sound recording speed. Adequate provision is made to adjust 
the projector and camera movements to the interlocking motor system. The 
coupling flange on the intermittent movement is so designed that it may be secured 
to the shaft in any position. It is necessary only to open two clamping screws, 
rotate either the motor or the intermittent movement shaft while the one or the 
other is standing, and clamp the flange tightly again after the proper position is 
attained in synchronism with the camera shutter movement. 

As in the case of regular projection room practice, it is necessary to adjust the 
lamp house to its correct position with relation to the aperture plate of the pro- 
jector, to see that the special condensing system is in its proper relative position, 
and that the arc is burning at its proper capacity in order to clear up the entire 
screen and attain satisfactory and uniformly distributed screen illumination. If 
a "hot spot" occurs at the center of the screen, it is possible to remove it by mount- 
ing a small circular disk cut from fine copper mesh exactly in the center of the 
light-beam at the proper point in front of the lens. Experiment will definitely de- 
termine the distances required with lenses of different focal lengths. 

There is, of course, very noticeable flicker upon the screen when using this type 
of projector, due to the single-bladed shutter that is used, so that it should not be 
used for normal projection of motion pictures. It is purely for process work, and, 
naturally, flicker is not noticeable to the synchronized camera under such circum- 
stances. Should it be required to project standard motion pictures with this 
equipment, the shutter must be removed and the standard two-bladed shutter 
substituted. The equipment, of course, must be carefully handled, due to its ex- 
treme accuracy, and if expert attention is given it, it will give excellent service for 
an indefinite period of time. 



RCA PHOTOPHONE HIGH-FIDELITY SOUND REPRODUCING 
EQUIPMENT* 



J. FRANK, JR.** 

In February, 1931, RCA Photophone introduced the first theater sound repro- 
ducing equipment operated entirely by alternating current. The rotary stabilizer 
sound-head attachment was introduced in December, 1932. Consistent develop- 
ment in the past four years in the improvement of reproducing apparatus has 
made possible the high-fidelity equipment. 

Improvements in sound-film recordings during the past year and planned for the 
near future require reproducer equipments having increased reserve power out- 
put for satisfactory results. To meet these requirements a new line of high- 
fidelity sound reproducing equipment has been introduced. Considerably in- 

* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** RCA Manufacturing Co., Camden, N. J. 



100 NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 

creased output, equivalent performance at lower cost, greater flexibility, and 
easier operation are all factors involved. The equipment is designed to repro- 
duce class A release prints (certain producers release class A and class B prints, 
the former with a reduced recording level permitting extended volume range) 
satisfactorily in auditoriums of all sizes. The high-fidelity equipment is offered 
on an outright or conditional sale basis. 

High-fidelity equipments are available with either a combined sound projector 
or with sound-head attachments for mounting with silent projectors. The sound 
projector is equivalent in performance to the Super Simplex silent projector. All 
the outstanding features of the high-fidelity sound-head attachment have been in- 
corporated in this projector. 

The sound projector and sound-head attachment employ a combined freely 




FIG. 1. Operating view of rotary stabilizer sound -head attachment. 

revolving gate and rotary stabilizer to maintain constant speed of the film past 
the scanning light. Driving motors for all forms of power supply are readily in- 
terchangeable. The use of precision ball bearings throughout provides a con- 
struction that is trouble-free and has very long life. 

The projector is available with a built-in incandescent lamp house for a 900- or 
1000-watt lamp, a 30-ampere low-intensity reflector arc lamp house, or a 45- 
ampere high-intensity reflector arc lamp house. Power conversion apparatus is 
also available at additional cost. In addition to the built-in lamp house, other 
features include a motor, built in for quiet operation, gear drive throughout, 
2000-ft. magazines, and a 3- or 5-point pedestal base. 

All amplifiers are a-c. operated. Each unit is self-contained, with its own 
power supply unit. Standard RCA Radiotron tubes are used throughout. 
Amplifiers are designed for uniform reproduction of 40 to 10,000 cycles per second, 



July, 1936] 



NEW MOTION PICTURE APPARATUS 



101 



with means for adjusting the response characteristic to compensate for audi- 
torium conditions and poor recordings. 

These equipments all employ separate voltage and power amplifier units. 
From several points of view, this is desirable. The voltage amplifier unit has 
sufficient power to overdrive the power 
amplifier, without appreciable distortion 
from the amplifier unit. If for any reason 
the power amplifier should fail, operation 
can be temporarily continued with the 
voltage amplifier unit alone. If there are, 
in the future, any marked improvements 
in the methods of recording, necessitating 
either extension of the frequency range or 
the need for increased power output, units 
can be added to or substituted for the 
present ones. 

The amplifier units are designed for shelf 
mounting; in a wall cabinet for the smaller 
equipment, and on standard channel-iron 
racks for the larger equipment. In the 
latter case, all the power equipment is 
mounted upon the rear panel, while the 
parts comprising the amplifier circuits are 
mounted upon a hinged shelf protruding in 
front of the rack. The hinged shelf feature 
permits easy access to all parts without the 
necessity of removing the unit from the 
rack. It also permits easy removal of the 
amplifier circuit portion alone. Capacitors 
are sectionalized and separately fused, 
which means that the failure of any one 
section will not cause sound "outage," but 
will merely cause slightly increased hum. 
The failure of the fuse can easily be deter- 
mined by the operator. These units also 
include neon indicator lamps in the plate 
circuits of the tubes for assistance in deter- 
mining the cause of failure of operation. 
Perforated panels are employed in front of 
amplifier tubes to permit quick inspection. 

The larger equipment employs a low-impedance photocell coupled circuit, per- 
mitting locating the amplifier at some distance from the projector. The small 
equipment employs low-capacity coupling, requiring mounting the amplifier upon 
the wall between the projectors. Changing over the amplifier input from one 
projector to the other is accomplished by a switch located upon the front wall at 
each projector station. With the larger equipment, provision for variable control 
of the photocell output level is also provided. A remote volume control device is 
available for the larger equipment at additional cost. 




FIG. 2. RCA Photophone sound 
projector. 



102 



NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 



A separate tube rectifier for supplying power to the loud speakers is furnished 
in a wall -mounting cabinet for location in the rheostat room. This unit furnishes 
d-c. excitation to a maximum of five speaker units upon the stage as well as cur- 
rent for the exciter lamps. In the smallest equipment, a-c. exciter lamps are used 
and speaker field excitation is derived from the amplifier circuit. For operation 
by direct current, rotary converters and starters can be supplied. 

Loud Speaker Equipment. The loud speakers are of the directional baffle type, 
with dynamic cone reproducing units. For the larger equipment a combination 
of straight baffle loud speakers for reproducing a range of 125 to 10,000 cycles per 
second and a folded baffle loud speaker for reproducing frequencies of 40 to 125 

cycles per second are furnished. The 
straight baffle loud speakers employ a 
6-inch dynamic cone unit. For large 
auditoriums, three or six are used, de- 
pending upon the size and shape of 
the auditorium. The low-frequency 
folded baffle loud speaker employs two 
8-inch dynamic cone units. This com- 
bination of loud speakers has an over- 
all depth of only 26 inches, and can 
be flown with the picture screen or 
mounted in a cage on a monorail. 

The high efficiency and directional 
characteristics of the loud speakers 
make it possible to cover the audi- 
torium uniformly, with minimum re- 
flection from walls and ceiling. An 
electric circuit cutting off the response 
of the low-frequency loud speaker be- 
low the range of the fundamental voice 
frequencies assures satisfactory in- 
telligibility. 

A compound directional baffle loud 
speaker, employing a single 6-inch 
dynamic cone unit, with an over-all 
depth of 21 inches is used with the medium -size equipment. Extended-range 
reproduction is attainable with this single loud speaker, which employs a 
straight horn for reproducing the high frequencies and an exponential horn for 
the low frequencies. 

A straight directional baffle loud speaker, employing a single 6-inch dynamic 
cone unit, having an over-all length of 37 inches, is furnished with the smallest 
equipment. A short metal directional baffle loud speaker, employing a perma- 
nent field dynamic cone unit with a separate volume control, is furnished for moni- 
toring purposes hi the projection room. 

Portable Sound Equipment. This consists of one or two portable sound projec- 
tors, a portable amplifier, and a portable loud speaker. The single projector 
equipment consists of three cases, one each for the projector, amplifier, and loud 
speaker. The double projector equipment consists of five cases, one each for two 
projectors, amplifier, loud speaker, and second upper magazine. 




\ 



FIG. 3. Triplet and low-frequency 
loud speaker combination. 



July, 1936] 



NEW MOTION PICTURE APPARATUS 



103 



Portable Sound Projector. The portable sound projector is available with 
either an incandescent lamp house for a 900- or 1000-watt Mazda lamp, or with a 
15-ampere, low-intensity reflector arc lamp. An a-c. exciter lamp is employed. 
Projectors are regularly furnished with a standard series 1 Bausch & Lomb 5-inch 
projection lens. Portable projector stands are available at additional cost. The 




FIG. 4. 



RCA Photophone portable projector with 
ampere arc lamp. 



15- 



over-all dimensions of the projector are 43 1 A X 13 X 44 inches; weight, approxi- 
mately 106 or 129 pounds. 

Portable Amplifier. The portable amplifier consists of a voltage amplifier unit 
and power amplifier unit neatly mounted in a carrying case in such a manner that 
all controls are readily accessible. Two receptacles are provided for the output 
of each projector. A jack is provided for a close-talking microphone or a phono- 
graph. 

The amplifier units are similar to those furnished with the PG-90 equipment. 
A tone control is included, for modifying the response. A 10-ft. power cable is fur- 
nished. The complete assembly of amplifier in case measures 18 X 19 X 11 
inches, and weighs approximately 52 pounds. 



104 NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 

Portable Loud Speaker. The portable loud speaker consists of an 8-inch dy- 
namic cone speaker unit mounted in a carrying case of such construction that it 
acts also as a baffle. Included in the case is a wooden reel which carries 100 feet 
of loud speaker cable, and provision is made also for carrying one 2000-ft. upper 
projector magazine. The completed unit is of very rigid construction, and ca- 
pable of handling the power output of the amplifier adequately. The unit in the 
case measures 20 X 19 X 12 inches, and weighs approximately 47 pounds. 

Upper Magazine Case. For double projector equipment, the second 2000-ft. 
upper projector magazine is furnished with a separate carrying case, measuring 
17 3 /4 X ISVie X 8 inches, and weighs approximately 20 x /2 pounds. 

Public Address and Sound Reinforcing System. The use of public address and 
sound reenforcing systems in theaters is becoming increasingly more gereral. 
The high degree of perfection attained in the presentation of sound motion pic- 
tures has created a public demand for greater perfection in the presentation of 
both stage shows and orchestral selections. 

RCA sound systems provide all the following facilities: 

(a) Sound reinforcement of stage program, involving installation of micro- 
phones in footlight trough, upon the stage, and in the orchestra pit, with loud 
speakers at the side of the proscenium arch. 

(6) Sound reenforcement of vaudeville performance or vocal solo, involving in- 
stallation of one or two microphones upon the stage or upon the organ console 
near the soloist, with loud speakers at the side of the proscenium arch. 

(c) Public address system for announcements, with microphone located in 
manager's office, loud speaker in auditorium. 

(d) Rehearsal address system, with microphone at director's position and per- 
manent or portable loud speaker upon the stage and in booths. 

(e) Stage manager's call system, with microphone at stage manager's position, 
and loud speakers in dressing rooms. 

Two portable public address equipments are available. The larger includes a 
velocity microphone with desk stand and suitable amplifier in one carrying case, 
and two portable loud speakers in second carrying case. The smaller includes a 
carbon microphone, amplifier, and loud speaker in a single carrying case. 

RCA Sonotone. This equipment is available with either bone-conduction or 
air-conduction instruments, connected to double-jack boxes mounted beneath the 
arms of the seats in the auditorium. A separate amplifier, placed across the out- 
put of an RCA amplifier, or connected to a magnetic microphone hung in front of 
the loud speakers upon the stage, is employed. 

RCA Trans-Lux. Arrangements have been made with the Trans-Lux Daylight 
Picture Screen Corporation for marketing their patented device which provides 
for rear projection equipment in conjunction with RCA Photophone equipment. 



July, 1936] NEW MOTION PICTURE APPARATUS 



105 



OPTICAL REDUCTION SOUND PRINTER* 



M. E. COLLINS** 



A new machine for optically reducing sound prints from 35 to 16 mm., known 
as the RCA PB141 optical reduction printer, is complete in itself with all parts 
mounted upon the main casting, which in turn is mounted upon a base and 







FIG. 1. RCA model PBl 41 optical reduction printer. 



pedestal equipped with casters so that the unit may easily be moved. The unit 
may be used in this form, or the base and pedestal may be removed and the 
printer mounted upon a table. 

* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** RCA Manufacturing Co., Camden, N. J. 



106 



NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 



As normally supplied, the printer operates on a 220-volt, 3-phase supply, 50 or 
60 cycles. The printing lamp requires a low voltage ( 12 volts) d-c supply, which 
is not supplied as part of the printer. 

An important feature of the machine is the use of a rotary stabilizer mechanism 
for moving both the 35-mm. and 16-mm. film at constant speed past the point 
where scanning and printing are accomplished. The drums over which the films 
pass do not subject the film to abrasion as would possibly occur with a film gate 
type of construction. The stabilizer drum units are in no way mechanically 

connected to the film sprockets or other gear- 
driven mechanisms, thereby avoiding reac- 
tions from those sources that might impair 
the quality of the printed sound-track. 

On the left-hand side of the printer (Fig. 1) 
is located the 35-mm. film-propelling mecha- 
nism. The 16-mm. film-propelling mechanism 
is located at the right-hand side of the printer 
casting and is essentially the same as that 
used on the 35-mm. side. 

The feed reels are located at the top and 
the take-up reels at the bottom of the printer 
casting. The films are threaded with the 
emulsions facing each other. Immediately 
to the left of the 35-mm. film-driving 
mechanism is located the optical system that 
focuses the scanning beam upon the negative 
being printed. The optical system used to 
reduce the track in the proper proportion in 
both the horizontal and the vertical planes is 
located between the two films and is in the 
same horizontal plane as the illuminating 
optics. All optical adjustments are completed 
and sealed at the factory. The control panel 
is located directly below the optical system. 

The printer motor and the receptacle panel 
are mounted upon the back of the main 
casting (Fig. 2). The unit is intended to be 
operated in the darkroom, and is provided 
with a safety threading lamp. The back of 
the printer is completely enclosed, and all gears run in oil. A handwheel is 
provided at the back of the motor for testing the film motion before applying the 
power. A footage counter indicating 35-mm. feet is provided. 

The optical system projects an image of a portion of the moving 35-mm. sound- 
track upon the surface of the 16-mm. film, which image moves in the same direc- 
tion and exactly at the same speed as the 16-mm. film, so that no relative motion 
between the image and the 16-mm. film occurs. The 35-mm. track is illuminated 
by an aperture image, but this image is not narrow, as is the scanning slit used in 
reproducers. The scanning image is about 0.010 inch wide, and at a frequency 
of 10,000 cycles about 6 waves are imaged upon the 16-mm. film. The border 




FIG. 2. Rear view of printer. 



July, 1936] NEW MOTION PICTURE APPARATUS 107 

lines for either side of the sound-track of the 16-mm. film are produced by making 
the scanning mask for the 35-mm. sound-track longer than the standard 16-mm. 
track width. The edge of the scanning aperture adjacent to the picture frame is 
adjustable so as to compensate for any slight variation in location of the picture 
frame or picture frame lines that may have resulted when the 35-mm. sound print 
or negative was printed in a commercial 35-mm. printer. This permits blocking 
off such irregularities as might otherwise appear upon the 16-mm. sound print. 

A sufficient range of illumination is provided so that satisfactory reductions 
can be made from both variable-width and variable-density records, whether 
negatives or positives. In general, the printer lends itself equally well to two types 
of reduction : 

(1} 16-mm. prints directly from 35-mm. negatives or duplicate negative sound- 
tracks. 

(2) 16-mm. duplicate negatives from 35-mm. positive sound-tracks. 

Optically reduced 16-mm. sound-tracks are superior in quality to sound-tracks 
produced by processes involving contact printing. This is attributable, in 
variable-width work, to increased effective contrast of the negative; and, in both 
variable-width and variable-density work, to the absence of contact printing losses 
due to imperfect contact and slippage between negative and raw stock. Also, 
the printer is superior to those optical reduction printers that scan the 35-mm. 
film with a thin line of light without producing a printing image whose longitudi- 
nal magnification is equal to the ratio of the film speeds. In such printers, slit 
loss occurs similar to that occurring in recorders and reproducers. The PB141 
printer is free of such losses. 



THYRATRON REACTOR THEATER LIGHTING CONTROL* 

J. R. MANHEIMER** 



The reasons for the use of electronic tube control of theater lighting have been 
discussed previously by the writer in a paper 1 describing a rectifier tube con- 
trol employing reactances, such as was installed in the Center Theater at New 
York. The present paper deals with a type of board for accomplishing similar re- 
sults in a slightly different manner, which was installed in the Metropolitan Opera 
House, also at New York. 

The thyratron reactor equipment has several distinctive features. The first is 
automatic voltage regulation of each lighting circuit, to maintain a lamp voltage 
corresponding to the position of the intensity control. This makes it possible, 
without the series type of dimmer, to change the number and size of lamps on a 
particular circuit and yet maintain the same circuit voltage without readjusting 
the setting of the intensity control. 

The second is the method of pre-setting and maintaining proportionate fading 

* Presented at the Fall, 1935, Meeting at Washington, D. C, 
** E-J Electric Installation Co., New York, N. Y. 



108 



NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 



between pre-sets. The fader consists of a single unit which can be connected by 
means of the pre-set selector switch to supply excitation to any pair of pre-set 
master intensity controls, as shown in Fig. 1. A pre-set master, in turn, supplies 
the excitation to all voltage regulators in the individual control units associated 
with one pre-set. With the exception of a single switch having three positions 
located in each control unit, which disconnects the output of the voltage regulators 
and reconnects one of the voltage regulators to the rehearsal masters, there are no 
contacts between the individual unit and its associated tube panel. Some types of 



PBOPOETIONAL 
FADLR. 




PRESET SELECTOR. 
PU5H BUTTON SWITCHES 



PRESET 
CONTROLS 

FIG. 1. Schematic diagram of proportional fader and preset 
masters. 



tube-reactor control use individual fading devices for the separate circuits which 
are all mechanically connected together and driven simultaneously during the 
fading operation. Pre-set selector contacts are likewise duplicated for the in- 
dividual fading devices, in addition to the selector switches described above. 
Further, sliding contacts are generally used in the intensity control unit. 

Third, the speed of operation of the thyratron reactor system is extremely 
rapid, due partly to the absence of amplification between the intensity control 
and the tube unit supplying the direct current to the saturable reactor; and partly 
to the regulating characteristic of the tube unit, which applies overvoltage to the 



July, 1936] 



NEW MOTION PICTURE APPARATUS 



109 



saturable reactor until the voltage of the lighting circuit nearly corresponds to 
the voltage output of the voltage regulator intensity control. This forcing action, 
in connection with the saturable reactor, eliminates a large part of the sluggish- 
ness that has been associated with dimmers of the reactor type. 

Fourth, the saturable reactors are constructed so that the windings are com- 
pletely surrounded by iron. This is accomplished by using a four-legged core 
which shields the magnetic circuit from stray fields and the influence of neighbor- 
ing magnetic materials. The windings are also protected from damage by this 
construction. 

Referring to Fig. 2, the operation of the tube unit is as follows : The d-c. voltage 




J JATUBABLC BLACTOC. 



THYfcATCON TUBE UNIT 



FIG. 2. Schematic diagram of thyratron reactor tube unit. 



across the capacitor A is derived from the intensity control of the individual con- 
trol unit and rectified by one of the two circuits of the full-wave kenotron. The 
other half of the kenotron rectifies the voltage of the lighting circuit, and the recti- 
fied voltage appears across capacitor B. Capacitors A and B are connected in 
series with the grid of the thyratron, the output of which supplies direct current 
to the saturable reactor. The voltage across capacitor A "turns on" the cur- 
rent, while the voltage across capacitor B "turns off" the current of the thyratron. 
The algebraic sum of these two voltages regulates the direct voltage supplied to the 
saturable reactor so as to maintain a lighting circuit voltage equal to the output 
voltage of the intensity control voltage regulator. 

The phanatron is a half -wave rectifier, connected directly across the d-c. winding 



no 



NEW MOTION PICTURE APPARATUS IJ. S. M. P. E. 



of the saturable reactor to maintain the current constant in this winding during 
the negative half -cycle when the thyratron does not supply current. 

Potentiometer C provides an adjustment of the lighting circuit voltage when 
the intensity control is set at zero, while potentiometer D provides a similar ad- 
justment when the current is maximum. These adjustments are independent 
of each other, and need be made only when the equipment is installed, to compen- 
sate for variation in the impedance of the circuit wiring. The change in tube 



L. N 



BLACKOUT SWITCH 

STAGE 
MASTER. 



WHITE $, CED $*+i SQLtN -^ BLUE. 




^WITCMLS 

COLOR, 
MASTERS 



FIG. 3. Schematic diagram of stage rehearsal masters. 



characteristic resulting from aging or high operating temperatures does not neces- 
sitate changing the settings of the potentiometers, since the regulating action of 
the tubes fully compensates for these variations. 

The Metropolitan Opera House installation consists of two groups of apparatus 
the pilot controller and the reactor group. The pilot controller, shown in Fig. 3, 
is arranged so that all stage and house individual control units, rehearsal group 
masters, and constant circuit switches are located on the main section. The stage 
and house masters, color masters, scene masters, faders, pre-set selector push- 
button, and blackout switches are all on the master section shown at the right- 
hand side of the controller. The master is so located that the operator, while 
controlling the lighting, can observe the stage through an opening in the stage 



July, 1936] NEW MOTION PICTURE APPARATUS 111 

floor between the curtain and the footlights. The individual control in each hori- 
zontal row corresponds to circuits of separate color groups. The intensity control 
handles and switch handles are arranged in horizontal rows so that their relative 
positions can be readily seen. 

The individual control unit consists of three voltage regulators, one for each of 
three pre-sets, corresponding operating handles with intensity scales, a three- 
position selector switch, an "on-off" switch, and an indicating light. The wiring 
connections to the individual control units are made up in flexible cables attached 
to plugs. Receptacles for these plugs are located in horizontal wiring troughs. 

The saturable reactor has two a-c. windings, connected in parallel, on a four- 



Scan select Scene 
buttons /tadar 

' House 
master 




WorkUcjht, shunt, 

tnisc. switches 



FIG. 4. Master controller for theater light intensity, with thyratron reactor 

power control. 

legged core, and a d-c. winding around both the a-c. coils as indicated in Fig. 2. 
The a-c. flux circulates around the two center legs, and the d-c. flux passes from the 
center legs through the outside legs. The a-c. flux does not induce any voltage in 
the d-c. coil because it passes through the d-c. winding in both directions. Both 
the a-c. and the d-c. windings are around the same part of the magnetic circuit, 
which renders the d-c. flux very effective in saturating the reactor. 

The closed circuit formed by the a-c. coils prevents the induction of any transi- 
ent voltage in the d-c. winding, and eliminates the necessity of connecting a re- 
sistor across this winding to absorb transient energy. 

The saturable reactor is so designed that, in combination with the tube unit, 
the dimming characteristic is maintained unchanged with a four to one change in 
load. In other words, if the connected load is reduced to 25 per cent of the reactor 
rating, the lighting intensity will still correspond to the setting of the intensity 



112 NEW MOTION PICTURE APPARATUS 

control of the individual control unit. Saturable reactors are connected in the 
neutral of the circuit so that the lighting circuits are protected at all times in case 
of a ground. 

Line booster transformers are installed to increase the voltage supply and to 
compensate for voltage drop in the reactor at full load. The voltage output of the 
booster transformer is 10 per cent of the normal line voltage, which limits the no- 
load voltage of each circuit to 110 per cent of normal line voltage. Due to the 
automatic regulation of each circuit, the maximum voltage for connected loads 
between 25 and 100 per cent of the reactor rating will not exceed the normal volt- 
age. 

REFERENCE 

1 MANHEIMER, J. R., AND JOSEPH, T. H.: "Electronic Tube Control for 
Theater Lighting," /. Soc. Mot. Pict. Eng., XXIV (March, 1935), No. 3, p. 221. 



FOTO FADE, A CHEMICAL AND DYE MIXTURE FOR 
POSITIVE FADES* 



T. R. BARRABEE** 



Since the beginning of the motion picture industry there has been a need for a 
simple process for making positive fades on film being edited. Such a dye mixture 
is available in Foto Fade which easily produces dye fades on positive film. 

There has been constant research for this type of material, but without much 
success; but a material is now available which on test by most of the larger 
studios and laboratories in Hollywood appears to produce the desired result. 
The fade produced is quite neutral in color from the light to the dark end, and is 
more uniform in its change than the fade obtained by diaphragm manipulation in 
the camera. 

Two hundred grams of Foto Fade is dissolved in twenty gallons of water, care 
being taken to assure complete solution of the dye in the chemical mixture. The 
dye solution may be kept practically indefinitely in deep wood, glass, or rubber 
tank. The film, weighted at the lower end, is slowly immersed frame by frame 
until the complete length desired is covered by the solution. The film should be 
rinsed before squeegeeing with damp chamois cloth before drying. The maximal 
density of dye is attained in about one minute. 

Although the use of Foto Fade has been restricted mostly to the professional 
field up to the present, it is equally applicable to substandard films. Since few 
amateur cameras are equipped with variable shutter mechanisms, a material for 
the easy production of positive fades should be particularly interesting to the 
amateur. 

* Received Nov. 11, 1935. 
** Dye Research Laboratories, Los Angeles, Calif. 



COMMITTEES 

of the 
SOCIETY OF MOTION PICTURE ENGINEERS 

(Correct to June 20, 1936; additional appointments may be made at any time 
during the year as necessity or expediency may require) 



L. W. DAVEE 
A. S. DICKINSON 



ADMISSIONS 

T. E. SHEA, Chairman 
M. W. PALMER 
H. RUBIN 



H. GRIFFIN 
D. E. HYNDMAN 



O. M. GLUNT 
A. C. HARDY 



BOARD OF EDITORS 
J. I. CRABTREE, Chairman 



L. A. JONES 

G. E. MATTHEWS 



W. H. CARSON 
O. O. CECCARINI 



COLOR 

J. A. BALL, Chairman 
C. H. DUNNING 
R. M. EVANS 

A. M. GUNDELFINGER 



H. W. MOYSE 
A. WARMISH AM 



H. GRIFFIN 



H. BUSCH 

A. S. DICKINSON 

G. C. EDWARDS 



CONVENTION 
W. C. KUNZMANN, Chairman 

J. H. KURLANDER 
EXCHANGE PRACTICE 

T. FAULKNER, Chairman 
A. HIATT 
J. S. MACLEOD 



M. W. PALMER 



N. F. OAKLEY 
H. RUBIN 
J. H. SPRAY 



T. ARMAT 

G. A CHAMBERS 



A. N. GOLDSMITH 
A. C. HARDY 



HISTORICAL 

E. THEISEN, Chairman 
W. CLARK 



HONORARY MEMBERSHIP 

J. G. FRAYNE, Chairman 



G. E. MATTHEWS 
T. RAMSAYE 



H. G. TASKBR 
W. E. THEISEN 



113 



114 



COMMITTEES OF THE SOCIETY 



[J. S. M. P. E. 



E. HUSE 

K. F. MORGAN 



JOURNAL AWARD 
A. C. HARDY, Chairman 



G. F. RACKETT 
E. A. WILLIFORD 



J. CRABTREE 
R. M. EVANS 
E. HUSE 
T. M. INGMAN 



LABORATORY PRACTICE 

D. E. HYNDMAN, Chairman 
M. S. LESHING 
C. L. LOOTENS 
R. F. MITCHELL 



H. W. MOYSB 

J. M. NlCKOLAUS 

W. A. SCHMIDT 
J. H. SPRAY 



MEMBERSHIP AND SUBSCRIPTION 
E. R. GEIB, Chairman 



Atlanta 

C. D. PORTER 

Boston 

T. C. BARROWS 
J. S. CIFRE 
J. R. CAMERON 

Camden & Philadelphia 
H. BLUMBERG 
J. FRANK, JR. 

Chicago 
B. W. DEPUE 
J. H. GOLDBERG 
S. A. LUKES 
R. F. MITCHELL 



Cleveland 
R. E. FARNHAM 
J. T. FLANNAGAN 
V. A. WELMAN 

Hollywood 
J. O. AALBERG 
L. E. CLARK 
G. H. GIBSON 
C. W. HANDLEY 

E. HUSE 

F. E. JAMES 

G. A. MITCHELL 
P. MOLE 

K. F. MORGAN 
G. F. RACKETT 

Minneapolis 
C. L. GREENE 



New York 

G. C. EDWARDS 

J. J. FINN 

G. P. FOUTE 

H. GRIFFIN 

W. W. HENNESSEY 

R. C. HOLSLAG 

M. D. O'BRIEN 

F. H. RICHARDSON 

H. B. SANTEE 

T. E. SHEA 

J. L. SPENCE 

J. H. SPRAY 

Rochester 

E. K. CARVER 

Washington 
N. GLASSBR 

F. J. STORTY 



Australia 
H. C. PARISH 

Austria 

P. R. VON SCHROTT 

China 

R. E. O'BOLGBR 



Canada 

F. C. BADGLEY 

C. A. DENTELBECK 

G. E. PATTON 



England 

W. F. GARLING 

R. G. LlNDERMAN 
D. McM ASTER 

R. TERRANEAU 
S. S. A. WATKINS 



July, 1936] 



COMMITTEES OF THE SOCIETY 



115 



France 

L. J. DIDIEE 

L. G. EGROT 

F. H. HOTCHKISS 

J. MARETTE 

Germany 

W. F. BIELICKE 

K. NORDEN 

Hawaii 

L. LACHAPELLE 



T. ARMAT 

H. T. COWLING 



O. B. DEPUE 



D. P. BEAN 
F. E. CARLSON 
W. B. COOK 
H. A. DEVRY 



India 

H. S. MEHTA 
L. L. MISTRY 
M. B. PATEL 

Japan 

T. NAGASE 

Y. OSAWA 

New Zealand 
C. BANKS 



Russia 

A. F. CHORINE 

E. G. JACHONTOW 

Travelling 

E. AUGER 

K. BRENKERT 

W. C. KUNZMANN 

D. McRAE 

O. F. NEU 

H. H. STRONG 



MUSEUM 

(Eastern) 

M. E. GILLETTE, Chairman 

G. E. MATTHEWS T. RAMSAYE 

E. I. SPONABLE 
(Western) 
E. THEISEN, Chairman 

J. A. DUBRAY A. REEVES 

NON-THEATRICAL EQUIPMENT 
R. F. MITCHELL, Chairman 

E. C. FRITTS J. H. KURLANDER 

H. GRIFFIN E. Ross 

R. C. HOLSLAG A. SHAPIRO 

A. F. VICTOR 



C. N. BATSEL 
L. N. BUSCH 
A. A. COOK 
L. J. J. DIDIEE 



J. I. CRABTREE 
A. S. DICKINSON 



PAPERS 
G. E. MATTHEWS, Chairman 

M. E. GILLETTE H. B. SANTEE 

R. F. MITCHELL T. E. SHEA 

W. A. MUELLER P. R. VON SCHROTT 



I. D. WRATTEN 



PRESERVATION OF FILM 
J. G. BRADLEY, Chairman 
R. EVANS 
C. L. GREGORY 
T. RAMSAYE 



V. B. SEASE 
W. A. SCHMIDT 



M. ABRIBAT 
L. N. BUSCH 
A. A. COOK 
R. M. CORBIN 
J. A. DUBRAY 



PROGRESS 

J. G. FRAYNE, Chairman 
R. E. FARNHAM 
E. R. GEIB 
G. E. MATTHEWS 
H. MEYER 
V. E. MILLER 



R. F. MITCHELL 
G. F. RACKETT 
P. R. VON SCHROTT 
S. S. A. WATKINS 
I. D. WRATTEN 



116 



COMMITTEES OF THE SOCIETY 



[J. S. M. P. E. 



PROGRESS AWARD 
A. N. GOLDSMITH, Chairman 



M. C. BATSEL 




C. DREHER 


J. I. CRABTREE 




J. G. FRAYNE 




PROJECTION PRACTICE 






H. RUBIN, Chairman 




J. O. BAKER 


J. J. FINN 


R. MIEHLING 


T. C. BARROWS 


E. R. GEIB 


E. R. MORIN 


F. E. CAHILL 


A. N. GOLDSMITH 


M. D. O'BRIEN 


J. R. CAMERON 


H. GRIFFIN 


F. H. RICHARDSON 


G. C. EDWARDS 


J. J. HOPKINS 


J. S. WARD 


J. K. ELDERKIN 


C. F. HORSTMAN 


V. WELMAN 




P. A. McGuiRE 




PROJECTION SCREEN BRIGHTNESS 




C. TUTTLE, Chairman 




A. A. COOK 


W. F. LITTLE 


B. SCHLANGER 


A. C. DOWNES 


O. E. MILLER 


A. T. WILLIAMS 


D. E. HYNDMAN 


G. F. RACKETT 


S. K. WOLF 




H. RUBIN 






PUBLICITY 






W. WHITMORE, Chairman 




J. R. CAMERON 


G. E. MATTHEWS 


P. A. McGuiRE 


J. J. FINN 




F. H. RICHARDSON 




SOUND 






P. H. EVANS, Chairman 




M. C. BATSEL 


K. F. MORGAN 


R. O. STROCK 


L. E. CLARK 


O. SANDVIK 


H. G. TASKER 


F. J. GRIGNON 


E. I. SPONABLE 


S. K. WOLF 




STANDARDS 






E. K. CARVER, Chairman 




F. C. BADGLEY 


C. L. FARRAND 


G. F. RACKETT 


M. C. BATSEL 


R. E. FARNHAM 


W. B. RAYTON 


L. N. BUSCH 


H. GRIFFIN 


C. N. REIFSTECK 


W. H. CARSON 


R. C. HUBBARD 


H. RUBIN 


L. DE FEO 


E. HUSE 


O. SANDVIK 


A. COTTET 


C. L. LOOTENS 


H. B. SANTEE 


A. C. DOWNES 


W. A. MACNAIR 


J. L. SPENCE 


J. A. DUBRAY 


K. F. MORGAN 


A. G. WISE 


P. H. EVANS 


T. NAGASE 


I. D. WRATTEN 




N. F. OAKLEY 







STUDIO LIGHTING 






R. E. FARNHAM, Chairman 




W. C. KUNZMANN 


V. E. MILLER 


E. C. RICHARDSON 


J. H. KURLANDER 


G. F. RACKETT 


F. WALLBR 



July, 1936] COMMITTEES OF THE SOCIETY 117 

SECTIONS OF THE SOCIETY 

(Atlantic Coast) 

L. W. DAVEE, Chairman 
H. G. TASKER, Past-Chairman M. C. BATSEL, Manager 

D. E. HYNDMAN, Sec.-Treas. H. GRIFFIN, Manager 

(Mid-West) 

C. H. STONE, Chairman 

R. F. MITCHELL, Past-Chairman O. B. DEPUE, Manager 

S. A. LUKES, Sec.-Treas. B. E. STECHBART, Manager 

(Pacific Coast) 

G. F. RACKETT, Chairman 

E. HUSE, Past-Chairman K. F. MORGAN, Manager 
H. W. MOYSE, Sec.-Treas. C. W. HANDLEY, Manager 



FALL, 1936, CONVENTION 

ROCHESTER, NEW YORK 

SAGAMORE HOTEL 
OCTOBER 12-15, INCLUSIVE 



Officers and Committees in Charge 

PROGRAM AND FACILITIES 

W. C. KUNZMANN, Convention Vice-P resident 
J. I. CRABTREE, Editorial Vice-President 
G. E. MATTHEWS, Chairman, Papers Committee 
H. GRIFFIN, Chairman, Projection Committee 
E. R. GEIB, Chairman, Membership Committee 
W. WHITMORE, Chairman, Publicity Committee 



G. A. BLAIR 

A. A. COOK 

J. I. CRABTREE 

K. M. CUNNINGHAM 



LOCAL ARRANGEMENTS 

E. P. CURTIS, Chairman 

K. C. D. HICKMAN 

L. A. JONES 

G. E. MATTHEWS 



I. L. NIXON 
W. B. RAYTON 
E. C. ROLAND 
L. M. TOWNSEND 



E. R. GEIB 



REGISTRATION AND INFORMATION 

W. C. KUNZMANN, Chairman 

S. HARRIS 



F. E. ALTMAN 
E. K. CARVER 



J. G. CAPSTAFF 
E. K. CARVER 



A. A. COOK 
W. H. REPP 



TRANSPORTATION 
C. M. TUTTLE, Chairman 
J. G. JONES 

HOTEL ACCOMMODATIONS 

K. M. CUNNINGHAM, Chairman 
A. A. COOK 

PROJECTION 

H. GRIFFIN, Chairman 
E. C. ROLAND 



J. C. KURZ 
H. B. TUTTLE 



O. SANDVIK 
H. B. TUTTLE 



E. F. TETZLAFF 
L. M. TOWNSEND 



118 



FALL CONVENTION 119 

BANQUET 

I. L. NIXON, Chairman 

G. A. BLAIR R. M. EVANS S. E. SHEPPARD 

W. CLARK W. C. KUNZMANN H. B. TUTTLE 

A. A. COOK J. S. WATSON 

PUBLICITY 

W. WHITMORE, Chairman 

F. C. ELLIS J. C. KURZ G. E. MATTHEWS 

E. C. FRITTS E. C. ROLAND 

LADIES' RECEPTION COMMITTEE 

MRS. L. A. JONES, Hostess 

assisted by 

MRS. A. A. COOK MRS. C. M. TUTTLE MRS. H. B. TUTTLE 
MRS. R. M. EVANS MRS. S. E. SHEPPARD 

HEADQUARTERS 

The Headquarters of the Convention will be the Sagamore Hotel, where 
excellent accommodations are assured. A reception suite will be provided for 
the Ladies' Committee, who are now engaged in preparing an excellent program 
of entertainment for the ladies attending the Convention. 

Special hotel rates guaranteed to S. M. P. E. delegates, European plan, will 
be as follows: 

One person, room and bath $ 3.50 

Two persons, room and bath 6.00 

Parlor suite and bath, for two 10.00 

Parlor suite and bath, for three. . . 12.00 

Room reservation cards will be mailed to the membership of the Society in 
the near future and everyone who plans to attend the Convention should return 
his card to the Hotel promptly in order to be assured of satisfactory accommo- 
dations. Registrations will be made in the order in which the cards are received. 
When the Sagamore Hotel is booked to capacity, additional accommodations will 
be provided by the Hotel Arrangements Committee at another hotel in the 
immediate vicinity of the Sagamore. 

A special rate of fifty cents a day has been arranged for S. M. P. E. delegates 
who motor to the Convention, at the Ramp Garage, near the Hotel. 

TECHNICAL SESSIONS 

An attractive program of technical papers and presentations is being arranged 
by the Papers Committee. Sessions and entertainment programs will be con- 
ducted at the Sagamore Hotel and at the plants of the Eastman Kodak Co. and 
the Bausch & Lomb Optical Co. in accordance with the tentative program which 
follows. 

The attention of authors is directed to an announcement of the Papers Com- 
mittee at the bottom of the inside cover of this issue of the JOURNAL. Those 



120 



FALL CONVENTION 



[J. S. M. P. E. 



who contemplate submitting manuscripts for the Convention should communicate 
with the Papers Committee as promptly as possible. 

SEMI-ANNUAL BANQUET 

The Semi-Annual Banquet and Dance of the Society will be held at the Oak 
Hill Country Club on Wednesday, October 14th, at 7: 30 'P.M. Motor-coach 
transportation will be provided to and from the Club by the Transportation 
Committee. 

INSPECTION TRIPS 

Arrangements will be made on the days when the sessions are conducted at 
the plants of the Eastman Kodak Co. and the Bausch & Lomb Optical Co. to 
make tours of inspection of the plants. The members of the Society are also 
invited to be the guests of those companies at luncheon on those days. 



9:00 a. m. 



PROGRAM 
Monday, October 12th 

Sagamore Hotel Roof 
Registration 
Society business 



10:00 a. m.-12:00 p. m. 



Committee reports 
Technical papers program 



12:30 p. m. 



2:00 p. m.-5:00 p. m. 



8:00 p. m. 



Sagamore Hotel Main Dining Room 

Informal Get-Together Luncheon for members, their 
families, and guests. Brief addresses by several 
prominent members of the industry. 

Sagamore Hotel Roof 

Technical papers program. 

Eastman Theater 

"Color Photography" (with demonstrations and mo- 
tion pictures), Dr. C. E. K. Mees, Vice-P resident in 
Charge of Research, Eastman Kodak Co., Rochester, 

N. Y. 



Tuesday, October 13th 

The Convention will be in technical session on this day 
at the plant of the Eastman Kodak Co., at Kodak 
Park. Delegates will be the guests of the Eastman 
Kodak Co. at luncheon, and provision will be made 
for making a tour of inspection of the plant. 

The program for the evening of this day will be announced 
in a later issue of the JOURNAL. 



July, 1936] FALL CONVENTION 121 

Wednesday, October 14th 

The Convention will be in technical session on this day 
at the plant of the Bausch & Lomb Optical Co. 
Delegates will be the guests of the Bausch & Lomb 
Optical Co. at luncheon, and provision will be made 
for making a tour of inspection of the plant. 

7:30 p. m. Oak Hill Country Club 

Semi- Annual Banquet and Dance of the S. M. P. E.: 
addresses and entertainment. Motor-coach trans- 
portation will be provided to and from the Club by 
the Transportation Committee. Coaches will 
leave the Hotel promptly at 7:00 P.M. 

Thursday, October 15th 

10:00 a. m.-12:00 p. m. Sagamore Hotel Roof 

Technical papers program 

t 

2:00 p. m. Technical papers program 

Society business 
Adjournment of Convention 



SOCIETY ANNOUNCEMENTS 

STANDARDS COMMITTEE 

At a meeting of the Standards Committee held on June llth at the Hotel 
Pennsylvania, New York, N. Y., new drafts of the drawings for the revised issue 
of the Standards Booklet were carefully considered by the Committee, and the 
complete revision will probably be ready for the final action of the Committee 
within a few weeks. As announced previously, no change is being made in the 
content of the drawings, but an effort is being made to present the material in a 
more lucid and practicable fashion. 

PROJECTION PRACTICE COMMITTEE 

The last regular monthly meeting of the Committee was held on June 18th 
at the Paramount Building, New York, N. Y., at which plans to be followed by 
the Committee in the fall were discussed. Particular attention is being paid 
to the question of screen brightness and theater illumination, in collaboration 
with the Projection Screen Brightness Committee whose reports appeared in the 
May, 1936, issue of the JOURNAL. A study is being made also of the various 
state and municipal ordinances pertaining to motion picture projection, with 
the idea in view of paving the way toward greater uniformity in these regulations 
in the future. 

PACIFIC COAST SECTION 

On May 26th a joint meeting of the Pacific Coast Section of the S. M. P. E. 
and the Technicians Branch of the Academy of Motion Picture Arts and Sciences 
was held at the Metro-Goldwyn-Mayer Studios, at Culver City, Calif. 

Approximately 400 persons attended the meeting. Mr. Gerald Rackett, 
Chairman of the Pacific Coast Section, acted as chairman of the meeting, intro- 
ducing Mr. Douglas Shearer, Sound Director of Metro-Goldwyn-Mayer Studios, 
who conducted the symposium on "Essential Improvements Achieved in Sound - 
Film Recording and Reproduction in Adapting Conventional Methods to the 
High-Quality Requirements of Motion Pictures." 

During the symposium Mr. Shearer discussed the following subjects, illus- 
trating some of them by means of lantern slides or recordings: 

"Push-pull" recording and reproduction as a means of attaining increased 
volume range and minimum distortion. Variable- width and variable-density 
methods and Class A and Class B systems. Adaptation to stereophonic repro- 
duction. 

Side matting of sound-tracks; manual and automatic. 

Biasing methods; high-speed, carrier type, split-frequency, light-biasing. 

Valve ribbon travel frequency intermodulation. 
122 



SOCIETY ANNOUNCEMENTS 123 

Ultraviolet and monochromatic recording. 

Light-valve development and design. 

Halation studies. 

Complete re-recording of all release product as standard practice, and the 
choice of methods and standards for studio recording. 

Improved sound printer developments. 

Development of improved apparatus for moving sound-film without speed 
variation or flutter. 

The general reproduction problem in the theater. 

The Shearer two-way horn system. 

Amplifier requirements. 

Optimal reproducing scanning-slit width. 

Screens. 

The M-G-M automatic control system for production units. 

A new type of recording microdensitometer. 

In view of the fact that the meeting ran so late into the evening that there 
was no opportunity for discussion, an additional meeting was arranged for the 
evening of Tuesday, June 2nd, also at the Metro-Goldwyn-Mayer Studios. At 
this meeting Mr. Homer G. Tasker, President of the S. M. P. E., acted as Chair- 
man. About 150 persons attended and a very lively and interesting discussion 
ensued based upon many of the subjects covered by Mr. Shearer at the previous 
meeting. 



a new radio periodical 

RCA REVIEW 

A Quarterly Journal of Radio Progress 

Combining in one publication articles 
on the most significant technical 
developments in all branches of 
radio and its allied arts contributed 
by RCA and associated engineers. 

First appearance with July issue 
One year (4 issues) $1.50; outside U. S., $1.85 

RCA INSTITUTES TECHNICAL PRESS 

A Department of RCA Institutes, Inc. 

75 Varick Street -:- New York 



SOCIETY SUPPLIES 

The following are available from the General Office of the Society, at the prices 
noted. Orders should be accompanied by remittances. 

Aims and Accomplishments. An index of the Transactions from October, 
1916, to December, 1929, containing summaries of all articles, and author and 
classified indexes. One dollar each. 

Journal Index. An index of the JOURNAL from January, 1930, to December, 
1935, containing author and classified indexes. One dollar each. 

SMPE Standards. 'Reprints of SMPE Standards and Recommended Practice. 
Twenty-five cents each. 

Membership Certificates. Engrossed, for framing, containing member's name, 
grade of membership, and date of admission. One dollar each. 

Lapel Buttons. The insignia of the Society, gold filled, with safety screw back. 
One dollar each. 

Journal Binders. Black fabrikoid binders, lettered in gold, holding a year's 
issue of the JOURNAL. One dollar each. Member's name and the volume 
number lettered in gold upon the backbone at an additional charge of fifty cents 
each. 



JOURNAL 



OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXVII AUGUST, 1936 Number 2 

CONTENTS 

Page 

Report of the Projection Screen Brightness Committee 127 

Report of the Projection Practice Committee 140 

Report of the Standards Committee 145 

Report of the Committee on Preservation of Film 147 

Report of the Committee on Non-Theatrical Equipment 155 

Report of the Color Committee 164 

Improved Resolution in Sound Recording and Printing by the 

Use of Ultraviolet Light G. L. DIMMICK 168 

Primary Considerations in the Design and Production of 

Theater Amplifiers T. D. CUNNINGHAM 179 

Contributions of Telephone Research to Sound Pictures 

E. C. WENTE 188 

New High- Vacuum Cathode Ray Tubes for Recording Sound 
M. VON ARDENNE 195 

An Experimental Program in Visual Education 

F. H. CONANT 201 

Is the Federal Government Interested in Educational Films? 
C. M. KOON 204 

A Non-Theatrical, International Service Organization The 

Amateur Cinema League R. W. WINTON 210 

Physical Tests on Cellulosic Films, and Their Reproducibility 

S. E. SHEPPARD, P. T. NEWSOME, AND S. S. SWEET 218 

Committees 228 

Fall Convention at Rochester, N. Y., October 12-15, Inclusive 233 

Society Announcements 237 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors 
J. I. CRABTREE, Chairman 

O. M. GLUNT A. C. HARDY L. A. JONES 

G. E. MATTHEWS 



Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscriptions or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 

Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1936, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is 
not responsible for statements made by authors. 



Officers of the Society 

President: HOMER G. TASKER, Universal City, Calif. 

Past-President: ALFRED N. GOLDSMITH, 444 Madison Ave., New York, N. Y. 
Executive Vice-President: SIDNEY K. WOLF, 250 W. 57th St., New York, N. Y. 
Engineering Vice-President: LOYD A. JONES, Kodak Park, Rochester, N. Y. 
Editorial Vice-President: JOHN I. CRABTREE, Kodak Park, Rochester, N. Y. 
Financial Vice-President: OMER M. GLUNT, 463 West St., New York, N. Y. 
Convention Vice-President: WILLIAM C. KUNZMANN, Box 6087, Cleveland, Ohio. 
Secretary: JOHN H. KURLANDER, 2 Clearfield Ave., Bloomfield, N. J. 
Treasurer: TIMOTHY E. SHEA, 463 West St., New York, N. Y. 

Governors 

MAX C. BATSEL, Front & Market Sts., Camden, N. J. 

LAWRENCE W. DAVEE, 250 W. 57th St., New York, N. Y. 

ARTHUR S. DICKINSON, 28 W. 44th St., New York, N. Y. 

HERBERT GRIFFIN, 90 Gold St., New York, N. Y. 

ARTHUR C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

EMERY HUSE, 6706 Santa Monica Blvd., Hollywood, Calif. 

GERALD F. RACKETT, 823 N. Seward St., Hollywood, Calif. 

CARRINGTON H. STONE, 205 W. Wacker Drive, Chicago, 111. 



See p. 228 for Technical Committees 



REPORT OF THE PROJECTION SCREEN 
BRIGHTNESS COMMITTEE* 



In the May, 1936, issue of the JOURNAL there appeared a group of 
papers that set forth practically all the extant knowledge concerning 
the problem before this Committee. A brief re*sum of the state of 
our work is now in order. We, as a committee, are now in a position 
to evaluate the data at hand and to discuss the need for future 
work. In this report reference to the May issue will be made by page 
number for the benefit of the reader who wishes to inspect the evi- 
dence upon which any of our statements are based. The things we 
know are : 

The fundamental data of physiological optics are of questionable 
application to the screen brightness problem, because no work has 
ever been reported in which conditions existing in motion picture pro- 
jection are duplicated (Loivry, p. 490). The very complete bibliog- 
raphy of this paper (p. 500) is recommended to those wishing to study 
the data of visual functions. It is of interest to note that the data of 
visual acuity indicate definitely that all the detail customarily re- 
solved by the motion picture process is visible under what common 
sense and common experience tells us is a brightness much too low for 
visual comfort (Lowry discussion, p. 518). Since acuity is not a useful 
criterion of minimal screen brightness, other types of psychophysical 
tests are required. 

Of such tests we have some information in the paper by Luckiesh 
and Moss (p. 578), in the experiments reported by Wolf (p. 538), 
and in the experiment of O'Brien and Tuttle (p. 505). This latter 
experiment gives rather strong evidence of the desirability of a high 
brightness level about 30 foot-lamberts, as measured at the center 
of the screen with the projector running and with no film in the gate. 
Somewhat contrarily to expectation, the brightness level of screen sur- 
roundings does not affect the selected picture brightness in any con* 
siderable degree, but there is a marked preference for a surround- 
ing brightness greater than zero actually, about 0.05 foot-lambert is 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 

127 



128 PROJECTION SCREEN BRIGHTNESS COMMITTEE [j. s. M. p. E. 

preferred. This finding may be regarded as an important empirical 
contribution to the little-known subject of "glare" and its avoidance. 
The data of O'Brien and Tuttle indicate that a tolerance in the screen 
brightness of about =>= 50 per cent would be reasonable. This tolerance 
is based upon individual observer variation and scene subject varia- 
tion. 

The general conclusions of this empirical work are substantiated 
by the discussion offered by Luckiesh and Moss (p. 578) in which 
viewing motion pictures is compared to other visual tasks concerning 
which a greater mass of data is available. Some of the data quoted by 
Wolf (p. 538) place the desirable level somewhat lower. 

It is the desire of the Committee to adopt a critical attitude toward 
the work that has been quoted; not to cast doubt upon the results 
of the careful work of these authors, but rather to stimulate the repeti- 
tion of similar experiments by others. The importance of the sub- 
ject certainly justifies the expenditure of time by able investigators 
in the realm of physiological optics. 

In the case of the O'Brien-Tuttle investigation, the possible weak- 
nesses as pointed out by the authors are : 

(1) Actual theater conditions are not exactly duplicated. 

(2) Release print quality may not be represented accurately. 

(3) It is only inferred, not proved, that the brightness values se- 
lected by the observers are best from the point of view of avoidance 
of fatigue. Pending the completion of other work along similar lines, 
the Committee is inclined to accept the conclusions that the bright- 
ness level should be something of the order of 30 foot-lamberts, and 
that a peripheral brightness of the order of 0.05 foot-lambert is 
desirable at this brightness level. If such a brightness were attain- 
able, logical brightness limits would be 20 foot-lamberts minimal and 
45 foot-lamberts maximal. 

O'Brien and Tuttle have made the suggestion (p. 516) that the 
classical Weber-Fechner law may be applied to the problem. The 
argument presented, based upon the correlation of screen brightness 
of the highlight area with desired contrast, is one that should be 
followed up. 

We may now inquire regarding the factors not dealt with by these 
investigators that may affect the desired brightness level as deter- 
mined for the empty-running projector. In this connection, we have 
to consider only two factors, the human eyes and the release print 
densities. 



Aug., 1936] PROJECTION SCREEN BRIGHTNESS COMMITTEE 129 

There are not enough data on the effect of screen size (or subtended 
angle) on the influence of color of the reflected light, or on the in- 
fluence of auditorium illumination upon visual adaptation. Work 
along these lines should be encouraged by the Committee, although 
we can state that the magnitude of these effects is probably small. 

The possible effects of release print density we can evaluate more 
definitely. We ask, can the required brightness be lessened by mak- 
ing prints lighter? Would there be any improvement in picture 
quality if release prints were made denser? This procedure would 
require a brightness level even higher than that found by O'Brien 
and Tuttle for typical modern release prints. 

To the first question we can answer "no." Average release prints 
are being made as transparent as possible with existing photographic 
materials. Lighter printing would endanger tone reproduction in 
the highlight region (Tuttle, p. 553). 

To the second question we may answer "yes, but only by a slight 
amount." An increase of about 0.15 in the density of all release 
prints would place the highlight density of release prints on or near the 
straight-line portion of the positive characteristic in almost every 
case, and would probably improve tone reproduction. Supposedly, 
the required brightness would have to be increased about 40 per cent 
to afford optimal viewing conditions. 

The next point to consider is what screen brightness is possible. 
For that purpose we turn to the data of Cook (p. 530), who gives us 
the maximal brightness values attainable theoretically with ap- 
paratus and sources with their present practical limitations. As an 
example, we may draw upon his data to compute the conditions 
appertaining to a large screen with the best of modern projection 
equipment. We may assume for this purpose a 13.6-mm., high- 
intensity arc, a 5-inch //2.4 lens, and a diffuse reflecting* screen 25 
feet wide. The data in Table I are pertinent : 

TABLE I 

Lumens Available 5000 

Lumens Reflected 3750 (75% reflection assumed) 

Screen Area 469 square-feet 

Average Brightness 8 foot-lamberts 

* It is probable that only a diffuse screen would be satisfactory in any theater 
that would require a wide screen. Directional screens are of advantage only in 
narrow theaters. A directional wide screen will detract seriously from the bright- 
ness uniformity from side to side, especially for those seated to the side of the 



130 PROJECTION SCREEN BRIGHTNESS COMMITTEE [j. s. M. p. E. 

No projector optical system is capable of delivering uniform il- 
lumination. With a good system well adjusted, the distribution of 
brightness would be as given in Table II, for the stations indicated in 
Fig. 1. No more uniform values than these can be expected under 
actual operating conditions. 

TABLE II 

Station Brightness 

Foot-Lamberts 

1 9.6 

2 9.2 

3 8.1 

4 6.2 

As a rough approximation Table III shows the maximal brightness 
attainable with screens of different widths. The values apply to the 
center of the field, and again are based upon the best commercial 
optical systems in perfect adjustment. 

TABLE III 

Screen Width Center Brightness, Projector Empty 

Feet Foot-Lamberts 

30 6.7 

25 9.6 

20 15.0 

15 27.0 

These values represent optimal conditions, which are probably 
seldom fulfilled in practice. Reported greater central brightness for 
the given screen size is usually attained only at the sacrifice of over- 
all uniformity. 

Data given by Wolf for recent brightness measurements in theaters 
(p. 539) are not far out of line with these theoretical values, which 
fact shows that the projectionists, in general, are probably doing a 
good job. 

Now, the discrepancy between the desired value of 30 foot-lamberts 
and the maximum attainable with large screens will probably present 
a serious stumbling block in the way of standardization. An art or 
science in its progress toward perfection will, of course, resist an 
attempt to standardize if the standard has to be set at anything less 
than perfection. Since the beginning of the motion picture, when the 
optical system of the projector was a modified magic lantern and the 



Aug. , 1936 ] PROJECTION SCREEN BRIGHTNESS COMMITTEE 



131 



source was the lime light, there has been steady progress in the 
struggle to supply more light. An attempt was once made to stand- 
ardize at a brightness of the order of 2 foot-lamberts* (Wolf, p. 537). 
Such a recommendation, while it probably did little harm, certainly 
was of no value to the industry. What then are the possible virtues 
of standardization at the present time? 

The interest that has been shown in the activities of this Committee, 
both inside and outside the Society, is good evidence of the general 




FIG. 1. 



Stations for which brightness values have been 
computed. 



belief that there is room for improvement. We have heard comments 
upon all sides to the effect that a film that looks fine in one theater is 
very poor in another. Statements by Leshing (discussion, p. 543 s ) 
are very enlightening. Something is wrong if a picture printed in 
Hollywood is entirely satisfactory when reviewed there, but "was so 
bad as to be almost unrecognizable" when projected in another 



* Since the "recommended" value was "2.3 foot-candles on the screen," with 
none of the necessary conditions such as shutter or screen surface specified, the 
value of brightness may merely be inferred. 



132 PROJECTION SCREEN BRIGHTNESS COMMITTEE [j. s. M. p. E. 

theater. It is logical to hope that brightness standardization would 
remedy this situation. 

It appears to the Committee that the decision of whether or not to 
attempt standardization depends both upon the rate of improvement 
of projection optics and the possible rate at which improvements and 
inventions can be adopted by the theaters. Improvements in optics 
and projection sources are certain to take place, but it seems highly 
improbable that the available brightness will be doubled or tripled 
within the next few years. It will require time merely to bring existing 
theaters up to date in the matter of projection equipment, and no one 
can predict how rapidly improvements will be accepted in the future. 
We propose then to discuss a standard that must be regarded as tem- 
porary, because, for practical reasons, it must fall short of the ideal. 

For a standard admittedly based upon expediency, we are definitely 
committed to a value that is at least theoretically achievable by the 
majority of large theaters. We suggest the 30-ft. screen* as an arbi- 
trary limiting size, which the Society should attempt to bring within 
the pale of its recommendation. This sets the minimal brightness, in 
round numbers, at 7 foot-lamberts. We intend that this value shall 
refer to the center of the screen, and shall be measured with the 
projector running without film in the gate. 

Regarding an upper limit, there are two courses open. Recognizing 
the fact that our recommended minimum is far below the ideal, it 
might be logical to place the ideal of 30 as a top value. This proce- 
dure might not be satisfactory, for it might not lead toward sufficient 
uniformity from theater to theater. The second alternative is to set 
the top level at a value such that the quality of a release print ad- 
justed for projection at the mean level will not suffer if projected at 
either of the extremes. 

The experimental data needed by the Committee to fix a logical 
upper limit upon this basis will not be available for some time. This 
point will be mentioned again in connection with the future plans of 
the Committee. Briefly, the problem is to determine the brightness 
range throughout which the appearance of the picture is not materially 
altered by the brightness level. 

Application of the existing data relating to the Fechner fraction and 
brightness is a questionable procedure. Data of this nature have been 

* The Committee lacks certain statistical data regarding screen sizes in the 
United States. Also some data relating viewing distance with required screen size 
are pertinent. 



Aug., 1936] PROJECTION SCREEN BRIGHTNESS COMMITTEE 



133 



determined under restricted experimental conditions for photometric 
fields, and a somewhat different relationship between field brightness 
and contrast sensitivity may eventually be found for the viewing 
conditions of motion picture projection. 

Nevertheless, although the conclusions may not be entirely convinc- 
ing, it seems fruitful to make use of this material in an attempt to 
evaluate the effect of screen brightness upon picture contrast. From 
the data of Blanchard 1 we have constructed the curve shown in 
Fig. 2. This curve shows, for the brightness region in which we are 



























/ 






































/ 






































/ 








































/ 






































/ 






































/ 


/ 






















'A 
_ g> 
















/ 


























M 














/ 




































/ 




























sJL' 
r 










/ 






























X 

mft 








/ 


/ 






























"d 






/ 


/ 




































l 


/ 




































/ 


/ 




































/ 


/ 






































A T 





FIG. 2. Curve relating the Fechner fraction with field brightness. 

interested, the first derivative of the sensation/brightness relation 
as a function of log brightness. The ordinates have been adjusted to 
read in per cent of the maximal slope. In words, this curve gives us 
the value of the visual effect of the image brightness upon contrast. 
If we assume the Blanchard data to hold for the conditions of motion 
picture projection, we have a quantitative evaluation of the psy- 
chological factor which, when multiplied by the physical factor 
dD/d log E for the positive reproduction, will give us a new gradient 
applying to the appearance of the screen image at any level of bright- 
ness. 

In Table IV we have taken a series of values for empty-projector 
screen brightness and have computed from Tuttle's average release 



134 PROJECTION SCREEN BRIGHTNESS COMMITTEE [j. s. M. p. E. 

print data (p. 551) the brightness of various portions of the screen 
picture. In columns adjacent to the picture brightness values are 
given the value of slope taken from Fig. 2. These figures evaluate 
directly the subjective contrast effect. If, for instance, one looks only 
at the highlight of a picture, the subjective contrast is almost equal 
to the physical contrast, and changes only about three per cent as the 
empty projector-screen brightness is varied between 7 and 30 foot- 
lamberts. If one looks at the shadow, the apparent gamma is changed 
by about 50 per cent in passing from 7 to 30. If one is impressed by 
the brightness of the area of principal interest, the factorial variation 
is thirty per cent. For the average brightness, the variation is about 
thirty-five per cent. 

We have no entirely convincing data regarding the allowable con- 
trast variation. Certainly the discrepancies of individual taste will 
allow some tolerance. Indicative of the deviation from the selected 
contrast that is permissible, we may refer to laboratory practice 
in making release prints. Here a gamma variation of ten to fifteen 
per cent is usually allowed. 2 Presumably, this tolerance has been 
established upon the basis of a practical criterion of allowable varia- 
tion in picture quality. It is reasonable that the allowable subjective 
contrast effect of the screen brightness level tolerance should be of 
the same order. In other words, a picture should not appear more 
than 10 or 15 per cent more contrasty at the high than at the low 
level. 

Referring again to the derivative curve in Fig. 2, we find by inter- 
polation that for the highlight region, the maximum can not be 
high enough to affect contrast by as much as 15 per cent. 

For the shadow region, the subjective contrast varies so rapidly 
that if we formed our judgment upon this part of the picture, we 
should be able to allow scarcely any tolerance in screen brightness. 
It is probable, however, that the shadow area has very little sig- 
nificance in the evaluation of the picture contrast, since the extreme 
shadow region probably appears entirely black regardless of the 
screen brightness level (Lowry, p. 493) . 

Either of the other two values that of the average brightness or 
the brightness of the area of principal interest, is probably a good cri- 
terion upon which to base our subjective contrast tolerance. Re- 
ferring to these values, we find that the contrast increase amounts to 
about 7 per cent at 10 foot-lamberts and 15 per cent at 14 foot- 
lamberts. 



Aug., 1936] PROJECTION SCREEN BRIGHTNESS COMMITTEE 

TABLE IV 

Effect upon Visual Contrast of Various 
Screen Brightnesses for Various Parts of the Average Picture 



135 



Empty 
Projector 
Bright- 
ness (ft- 


High- 
light 
Bright- 
ness 


Contrast 
Seeing 
Ability 
dS 


Shadow 
Bright- 
ness 


Contrast 
Seeing 
Ability 
dS 


Bright- 
ness 
Principal 
Interest 


Contrast 
Seeing 
Ability 
dS 


Average 
Bright- 
ness 


Contrast 
Seeing 
Ability 
dS 


lamberts) 


(D = 0.43) 


d Log E 


(D=2.40) 


dLog J5 


(> = 1.0) 


d LogE 


(D = 1.15 


) d Log E 


7 


2.7 


0.97 


0.028 


0.33 


0.7 


0.75 


0.5 


0.69 


10 


3.7 


0.99 


0.040 


0.37 


1.0 


0.80 


0.71 


0.74 


14 


5.2 


1.00 


0.056 


0.41 


1.4 


0.87 


1.00 


0.80 


18 


6.7 


1.00 


0.072 


0.44 


1.8 


0.92 


1.28 


0.85 


22 


8.1 


1.00 


0.088 


0.46 


2.2 


0.94 


1.56 


0.88 


26 


9.6 


1.00 


0.104 


0.48 


2.6 


0.96 


1.85 


0.92 


30 11.1 


1.00 


0.120 


0.50 


3.0 


0.98 


2.13 


0.94 



CONCLUSION 

It appears to the Committee, in view of the arguments that have 
been presented, that the industry might stand to benefit by the adop- 
tion of a temporary screen brightness standard. Logical limits for 
such a standard would appear to be 7 foot-lamberts for the low value 
and 14 for the high value.* 

To recapitulate: The value 7 is based upon the value attainable for 
a diffusing screen about thirty feet wide with an efficient optical 
system in good adjustment. The value 14 is the limiting value be- 
yond which print contrast adjusted for the mean level of 10 foot- 
lamberts will appear too great. The values should be determined at 
the center of the screen with the projector running with no film in the 
gate. 

Even if the Standards Committee and the Society as a whole act 
favorably upon our suggested temporary standard, the Projection 
vScreen Brightness Committee regards its work as far from complete. 
We list below a few of the many problems that confront us. Some of 
these things we can work upon as a Committee; some call for long 
and painstaking research by qualified experts, results of which can best 
be given in the form of Convention papers. Some call definitely for 
the cooperative efforts of other Committees, especially the Projec- 
tion Practice Committee and the Laboratory Practice Committee. 

* This suggestion, if adopted, would set a logical standard for laboratory 
screening room practice. A mean value of about 10 foot-lamberts should be 
adopted, and tolerance in this value should be made as small as is compatible 
with practical limitations. 



136 PROJECTION SCREEN BRIGHTNESS COMMITTEE [j. s. M. p. E. 

We hope we shall earn the gratitude of future Papers Committees 
by listing these subjects for Convention papers. We hereby make an 
appeal for authors to undertake contributions designed to answer 
these questions: 

(1) What correlation is there between best print contrast and screen 
brightness ? 

(2) What effect does the brightness standard have upon the stand- 
ard of release print quality? Shall release prints of different contrasts 
be made available to theaters operating at different screen brightness 
levels ? (Any work done on the standard release print must, for ob- 
vious reasons, consider the screen brightness standard if it is adopted.) 

(3) Is highlight density, average density, shadow density, density 
of the area of principal interest, or a combination of these factors 
the thing that determines preferred brightness ? 

(4) What possibilities are there for improvement in projection 
optics, pull-down efficiency, and source brilliance? 

(5) What is the effect of color of the light-source, color of the screen, 
and color of the print upon the desired brightness? 

(6) What proportion of moving picture goers see pictures on screens 
greater than 20 feet, 25 feet, 30 feet? Statistical data on theater 
sizes, screen sizes, projection equipment, and attendance figures are 
needed by the Committee. A complete paper of this kind would be 
valuable also in connection with other problems confronting the 
Society. 

(7) What factors determine screen width ? Would it not be better, 
for instance, to use a 25-ft. screen at 9 foot-lamberts than a 30-ft. 
screen at 7 foot-lamberts ? The data of visual acuity tell us that the 
picture detail visible at great viewing distances should not suffer. 

(8) What are the possibilities for the development of simple, rugged, 
and inexpensive brightness-measuring instruments? Can not a 
satisfactory simple brightness tester be developed with two fields, one 
at the higher and one at the lower brightness limit? Could not 
such an instrument be used easily by the theater projectionist to de- 
termine whether he is operating within the recommended brightness 
range ? 

(9) What is the effect of auditorium illumination upon the re- 
quired brightness level? 

(10) What is the effect of the visual angle or the screen size upon 
this value? 



Aug., 1936] PROJECTION SCREEN BRIGHTNESS COMMITTEE 137 

(11) What tolerance in non-uniformity of screen brightness from 
center to edge should be established? 

C. TUTTLE, Chairman 

A. A. Cook W. F. LITTLE B. SCHLANGER 

A. C. DOWNES O. E. MILLER A. T. WILLIAMS 

D. E. HYNDMAN G. F. RACKETT A. K. WOLF 

H. RUBIN 



REFERENCES 

1 BLANCHARD, J.: "The Brightness Sensibility of the Retina," Phys. Rev., XI 
(Feb., 1918), No. 2, p. 81. Note: Data by Konig, and Brodhun and Aubert 
have been found to be in good agreement with those of Blanchard. 

(See TROLAND, L. T.: "The Principles of Psychophysiology" (Vol. II), 
D. Van Nostrand Co. (1930), New York, p. 77.) 

2 Bulletin, Acad. Mot. Pict. Arts & Sci., July 27, 1935. 

3 Joint discussion of "A Review of Projector and Screen Characteristics, and 
Their Effects upon Screen Brightness," by A. A. Cook, and "An Analysis of 
Theater and Screen Illumination Data," by S. K. Wolf, /. Soc. Mot. Pict. Eng., 
XXVI (May, 1936), No. 5, p. 543. 

4 LITTLE, W. F., AND WILLIAMS, A. T.: "Resume of Methods of Determining 
Screen Brightness and Reflectance," J. Soc. Mot. Pict. Eng., XXVI (May, 1936), 
No. 5, p. 570. 

DISCUSSION 

MR. CARLSON: I am somewhat concerned about the possible interpretation 
of a recommended level of screen brightness dictated by the limitation of present 
lighting equipment rather than the dictates of good practice. It would seem 
that a technical committee inquiring into a matter of this sort would be con- 
cerned with what it believed to be best, and would set up its conclusion as an 
objective toward which industry, projector manufacturers, and others might 
strive. 

MEMBER: Will Mr. Tuttle please explain the translation from foot-lamberts 
to foot-candles? 

MR. TUTTLE: Answering Mr. Carlson's objection first; we have, of course, 
considered the possibility of making our recommendation upon the basis of what 
is best. But to recommend the impossible would be no real benefit to the industry. 
Those who attended the last Convention heard a very convincing discussion by 
Mr. Leshing that showed that a disadvantageous situation exists in the theaters 
today that should be remedied. As we can not remedy it in the best way possible, 
it seems to us that there should be a partial remedy, in the form of a temporary 
recommendation. In our report we emphasize the fact that it is a temporary 
recommendation, which we wish to see changed in the future. 

Answering the second question : the foot-candle is a unit of illumination, and 
is concerned with the quantity of light striking a surface. The foot-lambert is a 
unit of brightness, and is concerned with the quantity of light leaving a surface in 
a given direction. If a perfectly reflecting and perfectly diffusing surface were 
illuminated to an intensity of 1 foot-candle, it would have a brightness of 1 foot- 



138 PROJECTION SCREEN BRIGHTNESS COMMITTEE [j. s. M. p. E. 

lambert. Illumination values given in foot-candles, then, can be converted to 
brightness values (foot-lamberts) by multiplying the illumination by the reflec- 
tion factor of the surface. The factor would be about 75 per cent for a good diffus- 
ing screen. 

MEMBER: Has the Committee obtained any data as to the over-all variation of 
screens throughout the country? 

MR. TUTTLE : We have a great deal of that sort of data, obtained from various 
sources, but we do not know how reliable it is. Brightness measurements are made 
in so many different ways, and often the conditions under which the measure- 
ments are made are not specified. We do not know whether the projector was 
running or not; we do not know in what region of the screen the brightness 
measurements were made; we do not know what kind of instrument was used. 
There is a great lack of reliable data of this kind. An answer to your question 
would therefore be more or less a guess. I should say that the brightness varies 
probably between 2 and 25, in various theaters. 

MEMBER: In your opinion the over-all variation is excessive? 

MR. TUTTLE: I believe it is much in excess of what should be allowed. 

MR. TASKER: The Committee in its report recommends or specifies some more 
or less standard method of measurement that may be used in the theaters? 

MR. TUTTLE: Yes. We are making a recommendation, through one of the 
symposium papers, 4 although more work must be done on the subject. It would 
be very fine if we could have some new brightness-measuring instruments especially 
designed for the purpose. 

MR. JOY: Were the values given by Mr. Tuttle average values over the whole 
screen, or merely the values at the center of the screen? If they were the average 
values, what consideration has been given to the distribution of the light upon the 
screen? 

MR. TUTTLE : The values quoted were for the screen center. Distribution has 
been considered, but perhaps not at sufficient length. We have shown in Fig. 1 
what we believe to be very good distribution. 

MR. CARLSON : In that connection, would it not be better to define acceptable 
brightness uniformity in terms of rate of change of brightness, or brightness 
gradients rather than in terms of an over-all change such as from the center 
to the corners. 

MR. JONES : Is not that what was done ? The values are given at various points ; 
that determines the gradient. 

We realize, of course, that it is undesirable to fix a standard below what we 
believe to be the most desirable. However, we have the situation that identical 
release prints are going out all over the country, some of which are shown in theaters 
having screen brightnesses of 2 foot-lamberts and some having perhaps 25. That 
is a very undesirable condition. If we can not realize the ideal screen brightness, 
we shall be much better off at least to limit the range over which the brightness 
varies, and so cure this difficulty of a print's looking all right in one theater and 
very bad in another. 

We have to deal with a present situation, and can not wait several years until 
we get these screen brightnesses up to 30 or 40 foot-lamberts. We shall have to 
wait quite a while for that. In the meantime, we should do something to remedy 
a condition that now exists. 



Aug., 1936] PROJECTION SCREEN BRIGHTNESS COMMITTEE 139 

MR. GREENE: The theaters that would be most likely to have brightnesses 
below the 2 foot-lamberts mentioned would have so many other great and glaring 
faults that I believe they could be totally eliminated from consideration, par- 
ticularly in a case of temporary standards. 

MR. JONES : I do not believe that is quite true. In some of the finest theaters 
having excellent equipment, with screens 35 feet wide, these relatively low levels 
of screen brightness are found. 

MEMBER: Within the past month a survey of theaters in Los Angeles showed 
that three theaters, in a group, had intensities of 5 to 22 foot-candles, and all three 
were called de luxe houses. 

MR. TASKER: It has been stated that 5 foot-lamberts is the brightness of the 
Radio City Music Hall screen. 

MR. DEPUE: When news weeklies are shown at the Roxy they are nearly 
twice the size of the feature picture. Can anyone tell what is the actual size? 

MEMBER: I believe 44 feet. 

MR. JONES: Is it possible with that type of print to produce news release 
prints that might be somewhat more transparent than a standard release print? 

MEMBER: Not generally, because the release prints are made for use through- 
out the whole country, and the gamma and density of the prints are held closely 
to the values in production release prints. 

MR. BRENKERT: In the Hollywood theaters mentioned, were the screens all 
approximately the same size? Was the same type of light-source used in taking 
the pictures? Was the brightness calculated without projecting a picture? 

MEMBER: I did not take the pictures personally. The screens, I understand, 
were about the same size, with a very appreciable difference in the lengths of 
the throws. The house with the low brightness had a throw, I suppose, of about 
50 or 60 feet. 

MR. BRENKERT: It is important whether the light-sources were approximately, 
or anywhere nearly, the same the projection distances were so different. 



REPORT OF THE PROJECTION PRACTICE COMMITTEE' 



The Committee has embarked upon what is probably its most im- 
portant undertaking to date the establishment of standards for the 
installation and operation of visual and sound projection equipment. 
When this work is complete, and considered in connection with the 
standard projection room lay-outs already published by this Com- 
mittee, there will be available to the industry a valuable reference 
source covering the entire projection process. 

Heretofore, the design, installation, and operation of projection 
equipment have been seriously hampered by a multiplicity of varying 
local and state regulations, a majority of which are undoubtedly 
well intentioned but which sometimes reflect a regrettable lack of 
knowledge of the projection process on the part of their sponsors. 
This situation operates to defeat the best efforts of manufacturers, 
exhibitors, and projectionists to attain better projection results; 
and also permits the rather widespread use of decidedly inferior 
equipment and encourages sub-standard installation and operating 
practices. 

It is a not uncommon experience, for example, for a manufacturer 
to gain approval of his product in one state, whereas an adjoining state 
withholds approval and enforces changes in design that occasion un- 
necessary expense and impaired operating efficiency. Indeed, there 
very often exists a sharp distinction between state regulations and 
those promulgated by municipalities therein. Exhibitors are con- 
fronted with the same difficulties, and equipment having the approval 
of one city is often unacceptable to another city in the same state. 
Members of the Committee who have had long experience in prac- 
tical projection work are agreed that the absence, rather than the 
existence of specific regulations in many states is highly undesirable, 
because the conditions to be met in such territories frequently lie 
within the province of some local official whose personal opinions are 
not consistent with generally approved procedure. There may then 
develop friction between the authorities of a given municipality 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
140 



PROJECTION PRACTICE COMMITTEE 141 

wherein one division of the city government disagrees emphatically 
with another. 

The Committee has set for itself the task of establishing projection 
standards which, it is hoped, will be acceptable not only to the 
Society but also to the nationally recognized regulatory boards. This 
goal having been attained, such standards could be submitted to the 
Sectional Committee on Motion Pictures, of the American Standards 
Association. Should complete success crown the efforts of the 
Committee in this direction there still would be lacking means of 
assuring their adoption by the various states, cities, and towns. 
It is assumed, however, that the prestige and authority accruing to 
the standards through the approval of the aforementioned impartial 
and non-commercial organizations would exert a patent influence, and 
go far toward inducing favorable action by a vast majority of the 
authorities. 

The efforts of the Committee are naturally directed to improving 
the quality of the screen image and of sound; but this objective can 
be achieved only after painstaking consideration of the many di- 
verse elements involved in the projection process, ranging from the 
film stock itself, through the entire chain of visual and sound pro- 
jection equipment units, to the screen. Obviously, this task will im- 
pose a severe strain upon the resources of the Committee. To this 
end the Committee extends an appeal to the industry generally, and 
to the full Society membership in particular, for cooperation in sub- 
mitting any data having a bearing upon this investigation. Other 
committees of the Society interested in related subjects have already 
been informed of this program and have been asked to cooperate. 

The Committee, as a matter of technical coordination, will en- 
deavor to obtain from each branch of the industry information on pro- 
jection equipment and methods and their bearing on other devices 
and processes used by the industry. These data should be widely 
disseminated in all quarters where they may be used to advantage to 
increase efficiency and economy. 

Other topics that will continue to engage the close attention of the 
Committee are: 

(7) Further refinement and extension of projection room lay-outs for small, 
medium, and large theaters. 

(2) General auditorium lighting, a topic that invites particularly close atten- 
tion at this time as a result of the general marked improvement of projection 
light-sources during the past two years. 



142 PROJECTION PRACTICE COMMITTEE [j. s. M. p. E. 

(5) Determination of the correct mirror magnification ratio to obtain an ac- 
ceptably uniform spot for the standard projector aperture with the Suprex arc. 

(4) Illumination and sound transmission characteristics of the screen. 

(5) Types of screen masking. 

(6) Suitable starting acceleration of motors driving the projectors (avoidance 
of excessive strain and consequent damage to equipment and film). 

(7) Projection illumination with reference to color-film. 

The last topic is particularly important at this time because of the 
possible increasing use of color film by the industry. The resultant 
color upon the screen is dependent in large measure upon the light- 
source used and the accuracy with which it is controlled. Color- 
film projection merits special attention upon the score of both quality 
and quantity of the projected light. In the future, the Committee's 
recommendations concerning projection light-sources will bear specific 
notations as to their applicability to black-and-white or color pro- 
jection. 

The Committee is particularly interested in finding a suitable light- 
meter that may be distributed at a price reasonable enough to induce 
widespread use. Several sample meters are now under consideration. 

H. RUBIN, Chairman 

J. O. BAKER J. J. FINN P. A. McGuiRE 

T. C. BARROWS E. R. GEIB R. MIEHLING 

F. C. CAHILL A. N. GOLDSMITH E. R. MORIN 
J. R. CAMERON H. GRIFFIN M. D. O'BRIEN 

G. C. EDWARDS J. J. HOPKINS F. H. RICHARDSON 
J. K. ELDERKIN C. F. HORSTMAN J. S. WARD 

DISCUSSION 

MR. WITTELS: Not long ago a new theater was being built outside Minneapolis, 
and I gave the drawings of the projection room lay-outs to the architect, who 
immediately recognized their value. I believe he took the lay-out for the size of 
theater he was building, incorporated in it everything that was needed, and laid 
out the projection room as the Projection Practice Committee recommended. 
I think the Committee should know about it. 

MR. KENNEDY: The Projection Practice Committee deserves a lot of commen- 
dation. All this discussion about light-sources and screen brightness will have to 
be studied from the ground up and will have to be solved. There are many differ- 
ent kinds of theaters, types of seating arrangements, sizes of screens, projection 
distances, and so forth, that it seems almost impossible for manufacturers to make 
machines that will be suitable for all conditions that is, to provide a certain 
brightness of screen for any distance while the projectors and light-sources are 
all made more or less according to certain standards. 

As was stated in the report, there should be greater agreement among the 
States, which even now agree in respect to certain of the specifications. It is 



Aug., 1936] PROJECTION PRACTICE COMMITTEE 143 

for this body to establish specifications and to see that the States adopt them and 
adhere to them. Then the manufacturers could make their equipment conform 
to those specifications. 

MR. JONES: A great deal of the preliminary work of standardization has to 
be done by the technical committees. When a technical committee has reached 
a point at which it is ready to recommend a standard, the recommendation must 
go to the Standards Committee, which will then formulate the proposal in the 
proper manner. We are now in the course of doing that but, of course, it can not 
be done hastily. We must proceed in an orderly fashion. 

MR. HOVER: I agree that the matter should not be taken care of too rapidly; 
but I happen to supervise a visual instruction program for the division of safety 
and hygiene of Ohio, and, to our horror, we recently found out that more than 40 
high-school auditoriums had been built during the past three years, with the 
intention of installing sound equipment in them. The projection rooms that were 
provided are portable, and are 5 feet square and 7 feet high. 

MR. WILLIFORD : In the electrical manufacturing industry there is a very defi- 
nite program for legislating standards. There is a Uniform Legislation Committee, 
and a paid staff for inspecting bills presented to the various municipal and state 
legislative bodies, and when advice needs to be given to those law-making bodies, 
it is given to them. 

I am wondering whether this Society has made adequate provision for getting 
its standards into the proper hands and watching this legislation particularly 
with respect to the American Institute of Architects. In addition to the American 
Standards Association, we should certainly consider taking advantage of some 
of these other agencies. 

MR. GRIFFIN: It has been recommended that the Committee call the attention 
of the Association of Electrical Inspectors to the work it is doing to achieve uni- 
form regulations throughout the country. It is a very large organization, whose 
members have jurisdiction over practically all the theaters of the United States. 
This is an important step and certainly should result in the Committee's gaining 
prompt action. 

MR. MITCHELL: The Non-Theatrical Committee report touches upon some 
of the regulations that have been promulgated and applied recently in 16-mm. 
projection and non-theatrical projection generally. We are making quite a point 
of the desirability of the Society's recognizing the conditions and striving through 
some sort of recommendation for uniform legislation. I think the two Committees 
can work together very effectively on this problem. 

MR. CRABTREE: In connection with Mr. Williford's remarks, we had in mind 
the matter of getting together a sort of compendium of information relating to 
construction. About two years ago Dr. Jones and I met in conference at Rochester 
with representatives of the American Institute of Architects. The result was that 
we were requested to have some Committee or individual prepare the material 
and present it at one of our meetings, at which it would be discussed. After that, 
the idea was to present it at several of the regional meetings of the AIA, and after 
further discussion to publish it in their journal. 

We tried to proceed with the formulation of this compendium of information. 
Mr. Schlanger undertook to handle the architectural side, Mr. Wolf the acoustical, 
and Dr. Jones the optical. I have been trying to get the three together for the 



144 PROJECTION PRACTICE COMMITTEE 

past two years. Mr. chlanger has published two papers. Mr. Wolf handed me 
one yesterday, and I believe Dr. Jones will speak for himself. That is where the 
matter stands now, but the three papers have not yet been fused together. It 
is a desirable thing to do, because I believe we have sufficient information at least 
to prevent such terrific blunders from being made as have just been mentioned. 

MR. JONES: If you have comprehended what has gone on at this session you 
will realize why I have not prepared the paper. Much work had to be done, and 
the work of the Projection Screen Brightness Committee shows what was done. 
We can not pull solutions out of thin air, and there is no point in recommending 
practices without adequate foundations upon which to base the recommendations. 
We have made progress, as reference to the May JOURNAL will show, and when 
the paper is finally written, it will contain very valuable information. 

MR. McGuiRE: One of the important purposes of the Projection Practice 
Committee is to show the interrelation of the various activities of the industry 
to each other in such a way that the industry will more fully appreciate what the 
SMPE has been doing as a coordinating body. We must try to show the industry 
how necessary it is to have some organization function to pave the way toward 
solutions of the many practical problems in the various departments in the in- 
dustry. Motion pictures are not made in a single factory as is an automobile. 
They start out in a given place, go through many vicissitudes, and finally wind up 
at the theaters. At any point in their travels something can happen that will 
destroy all that the specialists of the Society have done to perfect them. 

At a recent meeting of the Atlantic Coast Section we had an excellent talk on 
the elimination of flutter. There were diagrams. There was no question that 
flutter had to be taken out. During the discussion it was pointed out that if the 
sprocket teeth of the projector were worn, there would still be flutter. What is 
the use of sound engineers taking out the flutter if it comes back into the 
theater by another avenue? 

Although the sound engineer is expected by this time to be a specialist in his 
particular work, he must take a lively interest in the other activities of the indus- 
try, so that when flutter is taken out by him, it will stay out. We are all depen- 
dent in the end upon the success of the industry as a whole, and anything that 
injures the quality of the finished product in any way will to that extent undo the 
work of other departments of the industry. 

Therefore, if we can cooperate more fully, coordinate more, demonstrate how 
necessary such coordination is, more interest will be taken in the Society and 
its technical committees. Exhibitors take very little direct interest in the Society. 
We have made a number of attempts to get them to attend these meetings but 
the response has been extremely limited. 

It is a tremendous job to show the industry clearly, and make it understand, 
how necessary it is to coordinate all these interrelated activities. We must have 
the cooperation of the industry itself. But we can not do a great deal until we 
get real financial support in this field, and we are not getting it. Mr. Williford 
spoke a little while ago about doing this and doing that all of which require 
considerable money. All the Projection Practice Committee can do, for instance, 
is to make recommendations, for inducing and directing legislation. Perhaps 
a more complete understanding of what we are doing will prompt the necessary 
cooperation of the industry and speed up the activities of the Society. 



REPORT OF THE STANDARDS COMMITTEE* 

During the past winter the main activities of the Standards Com- 
mittee have been confined to the preparation of a new Standards 
Booklet in which will be incorporated several corrections, and which, 
it is hoped, will present the standards in a more usable form. 

The Standards Committee is exceedingly fortunate in having the 
able assistance of Mr. G. Fried! who has consented to undertake a large 
part of the work of revising the drawings. Most of the drawings have 
been reviewed by the Committee, and the improvement in the man- 
ner of presentation is apparent to all. 

The two proposals mentioned in the last report of the Committee, 
have been put into practice, viz.: 

(1} That the Engineering Vice-President be requested to appoint several 
European members of the S. M. P. E. to the Standards Committee, in order that 
they may establish a direct liaison between this Committee and the European 
Committees. 

(2) That copies of minutes of the meetings of this Committee be sent not only 
to such foreign members, but also to the secretaries of other Societies interested 
in motion picture technology and standardization both here and abroad, and to a 
selected list of persons who might be expected to offer criticisms or suggestions. 

Acceptances have been received from the following foreign mem- 
bers appointed to the Standards Committee by the Engineering 
Vice-President : I. D. Wratten (England) ; F. C. Badgley (Canada) ; 
A. Cottet (France); L. N. Busch (Germany); L. de Feo (Italy). 

The unfortunate situation in regard to the 16-mm. sound-film 
standards appears to be clearing up to a great extent. The Dutch 
Standards Committee adopted the S. M. P. E. standards last fall, 
and on February 25, 1936, a meeting was held in London at the 
Middlesex Guildhall with Lord Riverdale as arbitrator to decide 
which standards should be adopted by the British Standards Insti- 
tution. On March 20, 1936, it was announced that the award had 
been made to the S. M. P. E. standards so far as the position of the 
sound-track goes. 

The chief items under discussion at the present time are as follows : 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 

145 



146 STANDARDS COMMITTEE 

(1) Screen Brightness. It is hoped that the series of papers pre- 
sented at the Fall, 1935, Convention by members of the Projection 
Screen Brightness Committee, under the Chairmanship of C. Tuttle, 
and published in the May issue of the JOURNAL, will offer some prac- 
tical basis for standardization. 

(2) 2000-Ft. Reels. The Standards Committee has given its initial 
approval and final approval to the 2000-ft. reel recommended by the 
Academy of Motion Picture Arts and Sciences. The announcement 
has been made, according to the rules of the Society, in the April, 
1936, issue of the JOURNAL, and we are awaiting discussion from the 
membership. If the communications in regard to this are substan- 
tially favorable, the matter will be submitted to the Engineering 
Vice-President, who will present it to the Board of Governors for 
approval. 

The deletion of the definition of "reel" as approximately 1000 feet 
of film from the official glossary is in the same situation. 

(3) 16 -Mm. Sound Lead. The German standard for the lead of the 
sound over the picture in 16-mm. sound-film is 27 frames. The 
S. M. P. E. standard is 25 frames. A compromise proposal of 26 
frames has received initial approval by the Standards Committee 
and will be submitted for final approval very shortly. 

E. K. CARVER, Chairman 

F. C. BADGLEY R. E. FARNHAM G. F. RACKETT 

M. C. BATSEL C. L. FARRAND W. B. RAYTON 

L. N. BUSCH H. GRIFFIN C. N. REIFSTECK 

W. H. CARSON R. C. HUBBARD H. RUBIN 

A. COTTET E. HUSE O. SANDVIK 

L. DE FEO C. L. LOOTENS H. B. SANTEE 

A. C. DOWNES W. J. MACNAIR J. L. SPENCE 

J. A. DUBRAY K. F. MORGAN A. G. WISE 

P. H. EVANS N. F. OAKLEY I. D. WRATTEN 



REPORT OF THE COMMITTEE ON PRESERVATION 

OF FILM* 

During the early part of last year, the Carnegie Foundation do- 
nated five thousand dollars for the purpose of studying methods of 
preserving film records. It was stipulated that this money was to be 
administered under an advisory committee named by the National 
Research Council, and that the study should be conducted at the 
National Bureau of Standards. 

A little later The National Archives transferred additional money 
to the Bureau for this purpose, and the project has been proceeding 
with interesting results. The membership of the advisory committee 
and the general nature of the project was covered in a paper presented 
by the Chairman last fall. 1 The present reference to the project 
seems necessary as a foundation for this report. 

The Committee on Preservation of Film met at the Wardman Park 
Hotel, Washington, on October 24, 1935, and agreed, rather than to 
set up a research project of its own, to act as a sort of review board 
for the work being done at the Bureau of Standards, each member to 
make such individual contribution to the work as he could. The 
Chairman conducted some correspondence with the members of the 
Committee, but devoted most of his time in this capacity with the 
Bureau. However, on April 16th the Committee met at Washington 
in an all-day session, with the following members in attendance: 
John G. Bradley, Chairman, J. I. Crabtree, V. B. Sease, W. A. 
Schmidt, A. S. Dickinson, C. L. Gregory, G. R. Goergens (substitut- 
ing for R. Evans). 

It is significant that with the exception of one member this meeting 
represented the full membership of the Committee. Meeting with 
the Committee were the following guests: E. K. Carver, of the East- 
man Kodak Company; H. T. Cowling and G. C. Henry, of The 
National Archives; B. W. Scribner, John R. Hill, J. E. Gibson, and 
Meyer Reiss, of the Bureau of Standards. 

The project outlined for the Bureau of Standards as reviewed by 
the Committee at this meeting is referred to as the "twelve-point 
program," as follows: 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 

147 



148 COMMITTEE ON PRESERVATION OF FILM [j. S. M. P. E. 

(7) The effects of humidity and temperature and rapid atmospheric changes 
upon nitrate and acetate film, to determine the optimum atmospheric conditions 
for storage and use of films. 

(2) Determination of the effects of residual hypo or other active materials in 
the film upon the stability of the film base and the image. Also study of refixing 
and washing to remove residual chemicals, to include study of the feasibility of 
using distilled water in final washing and the suitability of other available water. 
Finding best practice for fixation, washing, and drying. 

(3) Type of tempering unit required for bringing films from low temperature 
storage conditions to projection room atmosphere without condensation of atmos- 
pheric moisture. Also conditioning required to prepare films for return to storage 
atmosphere. 

(4) The value of camphor or other restoratives in the storage containers to 
retard the loss of flexibility. 

(5) The value of protective coatings and other treatments for prolonging the 
life of films; also methods of reconditioning old films. This to include study of 
surfacing films, cleaning compounds, and so forth. 

(6) The merits of hermetic sealing vs. vented containers in the storage of films. 

(7) Expansion and shrinkage of the base and the gelatin coating, with con- 
sideration to the adhesion of the gelatin to the base. 

(8) The type of material for film cores and containers, to find the material least 
affected by decomposition products of nitrate films and least likely to harm the 
film wound upon it. 

() The character of decomposition products or other gases given off by the 
films under different aging treatments. 

(10) The development of specifications for films to be stored. The require- 
ments to be based upon results of the studies of factors affecting the life of films. 

(11) A study of acetate negative base. 

(12) A study of the effects of light and heat upon motion picture film during 
projection. 

It should also be pointed out that the results of work done by the 
Bureau can not be published until officially released. We are glad to 
say, however, that nothing was withheld from the members of this 
Committee and that a full report will be published later. We are 
also happy to have the privilege of including in this paper the follow- 
ing preliminary report on this project, subject to revision after further 
study and experimentation. 

TESTING METHODS 

When the work was initiated there were no well known test methods 
for use in connection with films. Almost everyone realized that 
nitrocellulose film was unstable; but just how long it would last 
under optimum storage conditions, and what these optimum storage 
conditions were, no one knew. As for the cellulose acetate film, being 



Aug., 1936] COMMITTEE ON PRESERVATION OF FILM 149 

a comparatively new product, no records of natural aging were avail- 
able, and very little was known about its lasting qualities. Conse- 
quently, a large part of the Bureau's work had to be directed toward 
developing tests applicable to the problems at hand. This is more or 
less a continuous process, and new methods are constantly being 
developed. Several possible tests were tried which were later aban- 
doned. But the following explains to some extent a few of the more 
successful and useful tests, and gives a general idea of the work done. 

Folding Endurance. A small, hand-operated, Pfund type of folding 
machine was used. The film was cut into strips to fit the machine, 
heated in an oven for definite periods of time at 100C., then placed 
into the machine and folded back and forth until broken, the number 
of folds being counted. The nitrate samples showed the greatest 
loss, and after a comparatively short aging period became too brittle 
to test. The acetate samples retained a much higher percentage of 
their original folding strength, and at the end of no heating period did 
they show a loss as great as that of the nitrate samples. 

Loss of Weight. Samples of both nitrate and acetate film were 
heated for definite periods of time in a dry oven at 100C. These 
samples were weighed before and after the heating treatment, and 
the loss of weight determined. Both types of film showed a continued 
loss with longer heating periods, the loss of the nitrate being much 
greater. The acetate suffered its greatest loss during the first few 
hours, and showed only a slight decrease thereafter. 

Viscosity. In following the effects of accelerated aging upon both 
acetate and nitrate films one of the most useful chemical tests found 
so far is the measurement of viscosity. This test consists in dissolving 
a small sample of the film in a definite volume of acetone, and measur- 
ing the time of flow in an Ostwald viscosity pipette. The viscosity is 
determined by expressing the time of flow of the solution relative to 
the time of flow of the solvent, which, in this case, is acetone. Ac- 
cording to some authorities, for equally concentrated solutions (be- 
low certain concentrations) of long chain molecules like rubber and 
cellulose, the viscosity depends only upon the molecular weight. 
Consequently, any breakdown of the molecular structure should be 
detected by a lowering of the viscosity. 

Here, too, the nitrate samples showed a greater loss upon heating, 
showing almost complete decomposition at the end of a compara- 
tively short heating period. The loss sustained by the acetate was 
very small. These results were obtained from heat treatments in an 



150 COMMITTEE ON PRESERVATION OF FILM [j. S. M. p. E. 

oven-dry atmosphere. When the samples were heated in an atmos- 
phere of very high humidity deterioration was accelerated. 

pH Determination. The free acidity of the film samples was 
determined by making use of pH. pH is expressed as the negative 
log of the concentration of the hydrogen ion. The lower the pH, 
the greater the free acidity; the higher the pH, the lower the free 
acidity. Nitrate film showed a decrease in pH upon heating much 
greater than the acetate. The H of old deteriorated nitrate film was 
very low. 

Copper Number. This is a standard test used in determining the 
deterioration of the basic cellulose of paper and was made use of in 
the film experiments. It was found unsuitable for use with the ni- 
trate film, but worked very well with the acetate. The acetate 
samples showed a slight increase in copper number for the longer 
heating periods. 

Deterioration of Emulsion. In determining the probable causes of 
the deterioration of nitrate film, the effect of the loss of camphor was 
investigated. It was found that old deteriorated nitrate film still 
contained a fair share of its original camphor. This seems to indicate 
that the deterioration of nitrate film is not caused by its loss of cam- 
phor. It is a combination of other factors. Nitrate film is at its 
best an unstable product, and anything which tends to increase its 
oxidation and hydrolysis will hasten deterioration. There was found 
a close parallelism between the amount of NH 3 (ammonia), the H of 
the gelatin, and the viscosity of the base. 

Humidity and Temperature. The effects of humidity and tempera- 
ture and rapid atmospheric changes upon both types of film have been 
investigated. Rapid or extreme variations of temperature and hu- 
midity were found to be detrimental. Probably the best conditions 
for storage would be very low temperature and humidity. However, 
a temperature of 50F. and a 50 per cent relative humidity is recom- 
mended as reasonable for all practical purposes. 

Residual Hypo. It has been found reasonable to expect and 
demand a content of thiosulfate sufficiently low to give a negative 
test. This thiosulfate can be eliminated by washing in distilled 
water, and detection technic can be developed following well known 
methods. 

Tempering. Extensive or elaborate tempering units are not neces- 
sary. Tempering can be accomplished by means of a sealed con- 
tainer, preferably a small container for two or three reels at a time. 



Aug., 1936] COMMITTEE ON PRESERVATION OF FILM 



151 



Summary. All the above-given results attained so far show very 
much greater stability for the acetate film than for the nitrate, and 
while it is not possible to predict just how long the acetate would last 
under natural conditions it appears to be a very promising material 
for permanent records. The only point in which acetate seems less 




3 




r 


-. 


i 




J 


f 




k 


X 
| 


I 


| 


s 


t 




*!. 


= 


/* I 




s. 




a 




i-.t-l 





FIG. 1. Plan of film container. 



desirable than nitrate film is its susceptibility to changes in relative 
humidity. However, it is believed that the expansion and contrac- 
tion is not a serious problem under controlled temperature and hu- 
midity. Distortion difficulties formerly encountered apparently 
resulted from incorrect storage and use of the film, lack of air-condi- 
tioning, etc. Under plans set up for preservation of film in The 
National Archives Building, for example, this problem should be of no 



152 COMMITTEE ON PRESERVATION OF FILM [J. S. M. p. E. 

great importance. Other phases of the work being done at the 
Bureau of Standards will be reported on later. 

FILM CONTAINERS 

The Committee at the April 16th meeting gave considerable time 
to a study of film containers for the storage of nitrate film. In this 
study it was undertaken to render a specific service to The National 
Archives. Under plans adopted for film storage cabinets, individual 
compartments for single reels of film have been provided, with a 
maximum height of 2.5 inches. The limitations of height in the 
compartments necessitated either a rather shallow lid that would 
come off when pressure was set up inside the can, or a vented type of 
lid that would allow the pressure to escape while the lid stayed on. 
A container of the latter type has been designed by the Division of 
Motion Pictures of The National Archives, and samples have been 
constructed. This allows, first, a 0.7 square-inch ventage for ' 'breath- 
ing" purposes when the can is in a state of repose, and additional side 
vents of 1 square-inch capacity which come into play in case the lid 
is partly lifted by pressure on the inside of the can. Hermetic 
sealing for nitrate film was disapproved. The construction of the 
can is illustrated by Fig. 1 . 

During the afternoon the Committee visited the Bureau of Stand- 
ards, where one thousand feet of old and badly deteriorated film was 
placed into this can and set on fire after the lid had been securely 
clamped by strong iron bands. The iron bands, however, permitted 
the lid to lift approximately one inch, the dimensions simulating the 
compartments in the storage cabinets. Heavy white smoke issued 
from the vents in the side of the can for approximately four minutes, 
with considerable pressure. Other than a black residue being de- 
posited upon the inside of the can no other damage was noted. 

A second roll of film was placed into the same can, a little drier than 
the first roll, and again set on fire. Instead of smoke issuing from the 
can, a fire was started immediately and continued for approximately 
two minutes. The flame was thrown out in all directions for several 
feet, with great violence and noise. The pressure was so great that 
one side of the can was lifted, creating a vent in excess of the vent 
provided in the lid of the can. On this evidence the Committee 
concluded that the vents should be made slightly larger to take care 
of maximum violence resulting from combustion. 

The Committee gave thought also to the material from which the 



Aug., 1936] COMMITTEE ON PRESERVATION OF FILM 153 

can should be made. The Bureau of Standards had previously 
recommended that only acid-resisting material should be used, with a 
possible choice between stainless steel and aluminum. Although 
aluminum is resistant to oxides of nitrogen, its tendency to flake and 
dust and its susceptibility to abrasions mitigate against its use for 
storage of motion picture film. The Committee concluded, there- 
fore, that if aluminum were used the film should be enclosed in black 
photographic paper. Its preference, however, was for stainless steel, 
Pyrex glass, or some acid-resisting material other than aluminum. 

ACETATE NEGATIVE 

The question of the use of acetate negatives was given consideration 
by the Committee. The National Archives is interested in this as 
a basis for determining future policy in its choice between use of 
nitrate negatives or acetate. In view of the seeming stability of 
acetate film, its use for future duplications of archives seems advis- 
able. The question was asked, "Can the film manufacturers furnish 
acetate base for duplicating negatives?" It was the thought of the 
Committee that reasonable assurance can be given at this time for a 
practical acetate negative for use under controlled conditions set up 
by The National Archives. Its greatest weakness is its tendency to 
buckle and distort, which would necessitate special handling. The 
representatives of the film manufacturing companies promised to give 
further thought to a pre-shrunk base. 

MISCELLANEOUS 

The Committee recommended, in addition to the work being done 
at the Bureau, (a) that the phrase "preservation of film" be defined 
to include "preservation of film records" by all possible means, in- 
cluding duplication; (b) that caution be taken in removing all possi- 
ble dust from the film before handling, rewinding, etc.; (c) that further 
thought be given to renovation and salvaging of old motion picture 
film, restoration of faded images, etc.; (d) that careful chemical tests 
be made for injurious foreign matter before accepting film for storage 
and (e) specifications for processing and handling new film; (/) optical 
printers for shrunken film, (g) filing aids, storage of safety film, etc. 

The Committee extended its thanks to the National Bureau of 
Standards for its helpful contributions in the field of film preservation 
and for its fine spirit of cooperation with the Committee. 



154 COMMITTEE ON PRESERVATION OF FILM 

J. G. BRADLEY, Chairman 

J. I. CRABTREE R. EVANS V. B. SEASE 

A. S. DICKINSON C. L. GREGORY W. A. SCHMIDT 

T. RAMSAYE 

REFERENCE 

1 BRADLEY, J. G.: "Motion Pictures as Government Archives," /. Soc. Mot. 
Pict. Eng., XXVI (June, 1936), No. 6, p. 653. 

DISCUSSION 

MR. CRABTREE: The Society is greatly indebted to Captain Bradley for 
assembling the available data, and particularly for stimulating further research 
through the medium of the National Research Council. It is unfortunate, how- 
ever, that in designing the Archives Building, the space for storing records was 
placed above ground. The architects have ignored the possibility of aerial bom- 
bardment. It would seem desirable, if any additions are to be made to the 
Archives Building, that provision be made for storage underground at a distance 
beyond that penetrable by aerial bombs of a size such as we may imagine will be 
designed within the next, say, fifty years. 

Captain Bradley intimated that film records could be perpetuated, by duplica- 
tion, for the life of the human race. That is, of course, assuming that 100 years 
or more from now anybody will be interested in duplicating them. If we are 
concerned with perpetuating records for hundreds or thousands of years, it would 
seem that some consideration should be given to making records upon metal 
bands, such as gold or platinum, which could be buried underground. This 
would insure (hi the absence of vandalism) that the people 5000 years from now 
would have some sort of record; whereas it is doubtful, even with the scheme 
outlined by Captain Bradley, that they will have any record at all if we antici- 
pate the aerial wars that may possibly occur in the future. 

MR. MITCHELL: Are there any data as to the keeping qualities of collodion 
emulsion as compared to gelatin emulsions? I understand that there is a proposal 
that a special emulsion such as collodion be used for important records instead of 
gelatin. It would require more light for printing, but if the keeping qualities were 
more desirable, it would be worth while to make the effort. 

MR. BRADLEY: The Committee at the Bureau of Standards is made up of two 
chemists, a physicist, and two paper men. The project has been financed for a 
year, and we have enough funds left from the first year to continue for another six 
months. We hope to receive additional funds for carrying on the project for at 
least three years. The product you mention has not been made a part of the 
present project, but we hope to investigate it later. 

MR. MATTHEWS: In connection with the Franco-Prussian War of 1870, mili- 
tary dispatches prepared photographically on thin collodion sheets were sent out 
from Paris by pigeons. Dr. Bendikson, at the Huntington Library at San 
Marino, Calif., had occasion recently to examine those records, which were about 
65 years old, very carefully. He found that they were in an excellent state of 
preservation, and should keep for many, many years to come. His report is 
published in the Library Journal, 60 (1935), p. 15. 



REPORT OF THE COMMITTEE ON NON-THEATRICAL 
EQUIPMENT* 

The use of motion pictures for non-theatrical purposes has in- 
creased with such amazing rapidity that it is becoming quite difficult 
to keep up with the developments. The great increase has been in 
the use of 16-mm. film, particularly 16-mm. sound-film, which has 
been so rapid that 16-mm. motion pictures have just about reached 
the stage at which they can be called industrial and educational 
rather than merely amateur. 

16-Mm. Test-Film. While at least two companies are putting out 
16-mm. sound-films containing constant frequency and musical 
recordings, there has been experienced a growing demand for an 
official SMPE 16-mm. test-film similar to the 35-mm. test-film. 
Such requests have been received consistently from abroad, and in 
view of the situation existing with respect to the SMPE and the DIN 
standard, it is urged that the immediate production of an official 
SMPE 16-mm. sound and picture test-film would materially 
strengthen the prestige of the SMPE standard. The members of 
this Committee regard this matter as very important. 

Referring to the use of DIN prints on SMPE type machines, at 
least two American companies supplying 16-mm. sound projectors to 
foreign outlets have prism or mirror attachments. These attach- 
ments are available at very nominal prices, and permit DIN prints to 
be used on SMPE projectors. It is also reported that subjects 
normally printed according to the DIN standard can very often be 
obtained according to the SMPE standard. The Standards Com- 
mittee is endeavoring to remove the present unfortunate differences 
now existing between these two standards, and their activities are 
being followed most anxiously. The recent decision of the British 
Standards Institution to adopt the SMPE standard is most encourag- 
ing and it is hoped that an ultimate solution will soon be found for the 
adoption of a world standard. 

The Industrial Field. Motion pictures, particularly 16-mm. silent, 
have experienced greatly widened application in the industrial field. 
It was here that the full possibility of showing 16-mm. film to large 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 

155 



156 COMMITTEE ON NON-THEATRICAL EQUIPMENT [j. s. M. p. E. 

audiences was first realized. With the introduction of sound and 
with the availability of 16-mm. sound recording, processing, and re- 
producing equipment of extremely high precision, the use of 16-mm. 
sound-film for advertising purposes has increased tremendously. 
It is reported that one of the large concerns manufacturing motor 
cars has, for the past two years, spent a major portion of its entire 
advertising appropriation on the production and showing of 16-mm. 
talking pictures. The success of these showings has persuaded every 
leading motor-car manufacturer to employ talking pictures for busi- 
ness advertising. Many leading companies in other lines of endeavor 
have duplicated and are duplicating this same experience. 

Ordinances and Similar Restrictions. The extent of the use of 
movies for non-theatrical work may be gauged by the fact that 
numerous ordinances have been passed in various parts of the country 
regulating such showings, or projectionists have been faced with 
obsolete regulations intended to cover theatrical shows only. As 
may be expected, wide variation is encountered. Some ordinances 
recognize the difference between theatrical and non-theatrical show- 
ings, and especially recognize the fact that equipment approved by 
the Fire Underwriters imposes no hazard in projection, so that there 
is no legitimate reason for imposing restrictions. Such ordinances 
are, in general, eminently fair, while others are most restrictive. 

This matter is assuming such proportions that, in some localities at 
least, the situation is rather critical. Therefore, the following is 
offered with the thought that the Society might officially recognize 
the situation and perhaps sponsor a national movement to offset un- 
fair and restrictive legislation. Another suggestion is that the So- 
ciety offer a model ordinance that might be called to the attention of 
authorities contemplating the necessity of covering this field. At 
least the distinction between theatrical and non-theatrical uses should 
be clearly specified. 

For instance, the regulations in Jacksonville, Fla., are so restrictive 
that any person owning a sound projector or a silent projector of 
capacity greater than 500 watts is legally liable to a fine of $100 for 
showing pictures in his home if he does not have a $16 license. (An 
amendment passed August 28, 1934, and published in the Florida 
Times-Union, September 6, 1934, states that "projectors containing 
sound and amplification apparatus or light-sources exceeding 500 
watts shall not fall within the range of amateur projection.") 

The ordinance does not distinguish between 16-mm., 35-mm., or 



Aug., 1936] COMMITTEE ON NON-THEATRICAL EQUIPMENT 157 

any other width; it arbitrarily covers any sound projector, and fails 
to recognize that in many schools, for instance, teachers and even 
students operate 16-mm. projectors up to 1000-watt capacity in per- 
fect safety. 

In contrast to this, the Chicago ordinance may be cited as fairly 
recognizing the safety of 16-mm. projection due to the fact that the 
film is made of slow-burning (acetate) base. The following quota- 
tions from the Chicago code are self-explanatory. Ordinances, 
Article VII, Electrical Code, concerning non-professional motion pic- 
ture projectors and equipment, contain, among others, the following 
provisions : 

Section 1669. Definition: Miniature Non- Professional Motion Picture Projec- 
tor: A non-professional motion picture projector whose construction provides for 
the use of films of a width less than one and three eighths ( 1 3 /s) inches, which film 
is regularly supplied only as slow-burning (acetate cellulose or equivalent) film. 

Section 1674. Fireproof Booth Unnecessary: The location of a non-professional 
motion picture projector in a fireproof booth shall not be required. 

Section 1676. Permit Required: A permit for each location, as provided in 
section 1638 of this code, shall be first issued for the installation and use -whether 
permanent or temporary of any non-professional motion picture projector, 
except a miniature non-professional motion picture projector, and also except any 
projector installed in a location for projection elsewhere than in an assembly hall 
or an assembly room, provided that these exceptions shall not apply where the 
means afforded for connection to supply power are not in accordance with section 
1676. 

Section 1677. Licensed Operator Required: When located for projection in 
assembly halls or assembly rooms, non-professional motion picture projectors, 
except miniature non-professional motion picture projectors, shall be operated by 
licensed operators, as provided for in section 2776 of this code. 

Section 2776. Moving Picture Machine Operators License Required; Applica- 
tions for License; Examinations: It shall be unlawful for any person to operate a 
moving picture machine, or device for any public or private gathering without first 
having obtained a license as a moving picture operator in the manner hereinafter 
set forth ; provided, that this article shall not apply to the operation of any moving 
picture machines or devices of a miniature type for home, lecture, and similar purposes 
requiring 16-mm. slow-burning type film." 

Educational. A quarter-century ago in America, the pioneer 
automobilist found himself seriously handicapped by the absence of 
suitable roads. The highway authorities, when approached, replied 
that they saw no reason for building wider, straighter, and smoother 
roads for automobiles when practically no automobiles existed. No 
automobiles, no roads. It seemed like a vicious circle, from which 
there was no escape. Yet an escape was found. Today automobiles 



158 COMMITTEE ON NON-THEATRICAL EQUIPMENT [j. s. M. p. E. 

are numbered in the millions, and road miles have multiplied beyond 
the fondest dreams. 

A similar situation has prevailed with respect to the educational 
film. Some educators have demanded that commercial film pro- 
ducers guarantee an ample and perfectly correlated supply of teaching 
films before equipment and films are bought by the schools. The 
film producers have maintained that their production must be for a 
profitable market; otherwise there could be no production. The 
argument has also been put forward that the educators themselves 
do not know what they want in the line of educational films. Equip- 
ment manufacturers have tried to find a way out of this impass in 
order that the school market might be opened up for equipment sales. 

The solution seems very much the same as that of the automobile 
and the roads: a gradual process of adaptation. Film producers 
have gone into education. Schools have gone into film production. 
Equipment manufacturers have gone into both film production and 
education, and finally a common meeting ground has been found in 
such clearing house associations as the National Academy of Visual 
Instruction, which only recently merged with the Visual Instruction 
Section of the N. E. A. The final unification of all organized visual 
instruction forces in the United States in a single, well-knit organiza- 
tion promises an auspicious future for the organization. 

The step taken by the American Council of Education and the 
formation of the American Film Institute 1 in Washington have been 
the foremost steps of late to create a greater interest in the use of visual 
instruction materials. The Rockefeller Foundation in New York is 
sponsoring the more extensive use of films and 16-mm. equipment in 
the school curriculum. 

The Federal government is taking a very active interest in the use 
of motion pictures for educational purposes, and a number of reports 
have been prepared covering these investigations. A compact sum- 
mary of the present status of the Federal government's interest in 
educational films discussed the five-point aim of the Educational 
Council study, the ten steps necessary to reach the goal, and the five- 
point project of the American Youth Commission. 1 

The proposed American Film Institute which has already been 
started, has set out in several directions. In the first place, it is 
expected to compile in catalog form all the present available educa- 
tional material, according to how it fits into the curricula, and list 
them in a much simpler form than now exists. The American Film 



Aug., 1936] COMMITTEE ON NON-THEATRICAL EQUIPMENT 159 

Institute will be a central headquarters for information as to film 
material available, and within a very short period of time it will 
be necessary for schools all over the country merely to write to the 
headquarters in Washington for one catalog, which will give complete 
information regarding all films available and upon what basis: 
rental, purchase, free, etc. There are several other endeavors, of 
course, of the American Film Institute, such as increasing the use of 
motion picture equipment as an instructional medium, organizing 
data relative to the present use of the equipment in the school market, 
how extensively 16-mm. sound is being used, whether sound or silent 
equipment is best suited for teaching purposes, etc. 

The Educational Screen, in coordination with the Department of 
Visual Instruction of the N. E. A., has recently sent out a question- 
naire to a large group of school principals throughout the country, 
asking what type of material they use; how they use it; what reasons 
they have to offer as to why visual instruction does not progress in 
their school system, if it has not; what suggestions they have for 
creating a greater interest in the use of visual aids; and many other 
such questions. The United States Department of Education, under 
Mr. Studebaker's signature, is also sending out a questionnaire to 
superintendents all over the country, asking similar questions, to get 
a good picture of the visual instruction situation in the United States 
at the present time. 

According to an excellent and comprehensive survey recently 
completed by Dr. F. E. McCluskey, 2 there are approximately 205 to 
225 visual instruction departments in municipal school systems, the 
equipment of which varies all the way from six dozen slides to such 
splendidly administrated resources as we find in the City of Phila- 
delphia. 

State visual instruction centers are usually sponsored by the state 
universities, but sometimes administered by the State Department of 
Education. There are approximately 28 such centers. Ten years 
ago 16-mm. educational film was practically unknown, but it now 
practically outranks the older 35-mm. material in all the more ad- 
vanced state centers. 

Museums, both city and state, frequently maintain extensive film 
service. Twenty-two such museums are listed by the National 
Academy of Visual Instruction. The largest among them is the 
New York Museum of Natural History. 

Individual school libraries are being built up in a number of centers 



160 COMMITTEE ON NON-THEATRICAL EQUIPMENT [j. s. M. p. E. 

on the correct theory that motion picture film should be instantly 
accessible, just as maps or reference books. 

Federal government departments such as the Bureau of Mines, 
Department of Agriculture, Department of the Interior, etc., offer free 
films to schools. The Navy Department offers free 16-mm. disk talkie 
films. 

Equipment manufacturers have built up libraries of informational 
films, generally with the cooperation of educational authorities. 
Films such as Raymond L. Dittmar's Living Natural History Series, 
made by the Curator of the Bronx Zoological Garden, and other such 
series, are now available. Commercial producers of teaching films do 
not, as a rule, rent or loan the films to schools, but offer their products 
for outright sale. 

Commercial sources of "free" films and other visual aids are exceed- 
ingly numerous. 5 General Electric Company offers a 32-page illus- 
trated catalog, free. Goodyear Tire and Rubber Company, Cater- 
pillar Tractor, Petrolagar, and other such commercial concerns make 
their films available gratis to school systems. The larger automobile 
companies, such as Chrysler, Pontiac, Hudson, General Motors, 
Fisher Body, and many others, likewise have new 16-mm. sound-films 
available free to schools. The distribution of commercial films is 
generally handled by sponsors such as the Y. M. C. A., National 
Council Motion Picture Bureau, etc. 

A number of productions have been made specifically to fulfill the 
requirements of the educational field. In this country the subjects 
put out by Erpi, in conjunction with the University of Chicago, have 
achieved international recognition. A development in France was 
recently reported 6 on the making of concert picture shorts. These 
shorts are made in duplicate, of eminent artists such as Paderewski, 
Kreisler, and others. One picture is accompanied by artistic scenes 
to enhance the mood of the music, while the other is a technical pic- 
ture showing the musicians' fingers, etc., to demonstrate to advanced 
students the technic involved. The Committee has reported 
previously the work done on extracting certain episodes from 
standard motion picture releases and re-editing them to form sub- 
jects of educational nature. This idea is apparently progressing, 
and would seem to present many possibilities if handled effectively. 
At the same time, the conviction is growing that the best educational 
subjects are those that have been specifically designed and made to a 
carefully worked out pedagogical script. 



Aug., 1936] COMMITTEE ON NON-THEATRICAL EQUIPMENT 161 

There is no longer any division of opinion as to whether 16-mm. or 
35-mm. equipment should be used in the schools. Although formerly 
35-mm. was used solely, it is now very rapidly being supplanted by 16- 
mm. Such large school systems as those in Los Angeles, San Diego, 
Chicago, and many others that formerly used 35-mm. are now using 
16-mm. apparatus exclusively. The February, 1936, Convention of 
the N. E. A. was especially enthusiastic about visual education in 
general and movies in particular. 

It is interesting to know that the motion picture has been used in 
the school ever since film existed. In fact, the motion picture owes its 
birth to educational and scientific research, rather than to the theater. 
However, the theater's claim to the film proved so much more profit- 
able than that of the school that the theatrical field very soon eclipsed 
the educational market. Prior to the event of the 16-mm. film, the 
attempt of the educator to use motion pictures ran into too many 
obstacles for it to become a large factor in the school market. How- 
ever, since the advent of 16-mm., all the obstacles of fire hazard, 
improper material, inadequate equipment, heavy equipment, etc., 
have been eliminated, and these have been the largest contributing 
factors for the very extensive use of motion pictures in the schools at 
the present time. 

Libraries. The growth of 16-mm. libraries, particularly sound- 
film, is extending rapidly, and already many hundreds of 16-mm. sound 
subjects are available for rental. Reports indicate that in the near 
future many thousands of such subjects will be available; the growth 
and use of 16-mm. sound-film for educational, industrial, and enter- 
tainment purposes has increased so very rapidly that wide-awake 
producers are becoming more and more alive to the possibilities of this 
field. 

Standards. There seems to be a satisfactory agreement between 
all members of this Committee, representing various manufacturers, 
that the following proposal be presented to the Standards Committee 
for consideration either as a standard or as a recommendation for 
approved practice : 

A screen intensity of 6 foot-candles is satisfactory for sub-standard projection 
where a screen of relatively high specular reflection is employed (for example, a 
beaded type of screen). An intensity of 10 foot-candles is recommended for the 
satisfactory projection of sub-standard pictures when using a screen of diffusing 
characteristics (such as a matte white screen). The figures given cover the 
projection of black-and-white film of average density. 



162 COMMITTEE ON NON-THEATRICAL EQUIPMENT [J. S. M. p. E. 

The same intensities are regarded by some members of the Com- 
mittee as satisfactory for the projection of 16-mm. Kodachrome, but 
it would seem desirable to suggest at least 8 and 12 foot-candle intensi- 
ties respectively for such applications. In this connection, reference 
is made to Fig. 1, covering the relation between screen size, foot- 
candle intensity, and total screen lumens. 

Considerable work has been done by the Committee on Non- 
Theatrical Equipment in investigating the various suggestions and 
recommendations made as to the methods of rating 16-mm. projec- 
tors. It is generally conceded that some sort of rating by means of 



j Z t l ti 3 J<f 31 3J-4 4? 4{ 4} 5 sj fj SJ 6 




FIG. 1. Chart of screen illumination and screen width. 

total screen lumens, measured under carefully standardized condi- 
tions, represents the most equitable form of rating. The objection, 
however, is raised that such rating is relatively unfamiliar to most 
persons, and that there is not yet any agreement as to the methods 
to be employed in making such rating. The suggestion is offered 
that the foregoing foot-candle specifications, while not affording 
complete specification, do cover the practical requirements of the non- 
theatrical field in a satisfactory manner. Foot-candle meters of 
reasonable, accuracy are widely available, and it is a relatively simple 
matter to measure foot-candle intensity with sufficient accuracy for 
average practical purposes. It is accordingly recommended that 
each projector manufacturer furnish data in the form of curves, 



Aug., 1936] COMMITTEE ON NON-THEATRICAL EQUIPMENT 163 

tables, or as he may otherwise see fit, giving the sizes of screens recom- 
mended for use with the various models of his projectors with the two 
general types of screen suggested. 

It is rather felt by the various members of this Committee that a 
general recommendation of this type not only covers practical re- 
quirements satisfactorily, but avoids arbitrary ratings of projectors 
that might be interpreted to the detriment of some particular prod- 
ucts. In other words, some preliminary form of standard is deemed 
desirable, but complete and restrictive specifications should not be 
made until the subject has been investigated more exhaustively. 

R. F. MITCHELL, Chairman 

D. P. BEAN H. A. DEVRY R. C. HOLSLAG 

E. W. BEGGS E. C. FRITTS E. Ross 

F. E. CARLSON H. GRIFFIN A. SHAPIRO 

W. B. COOK A. F. VICTOR 

. 

REFERENCES 

1 "Films in Schools," Motion Pict. Herald, Jan. 18, 1936, p. 18. 

2 "Visual Education," Mot. Pict. Prod. & Distr. Amer. (New York, N. Y.), 1932. 

3 GRAY, H. A.: "The Educational Motion Picture of Yesterday, Today, and 
Tomorrow," School of Progress, Toronto, 4, No. 2. 

4 Report of the Committee on Non-Theatrical Equipment, /. Soc. Mot. Pict. 
Eng., XXIV (Jan., 1935), No. 1, p. 26. 

6 KOON, C. M.: "Sources of Educational Films and Equipment," U. S. Dept. 
Interior, Dept. of Education, Circular No. 150 (Feb., 1936). 

6 "Concert Picture Shorts," Variety, 121 (Jan. 22, 1936), No. 6, p. 1. 



REPORT OF THE COLOR COMMITTEE* 

The Committee submits herewith a supplement to the original 
Glossary of Color Photography 1 in which a few terms are redefined 
and a few new ones added. 

In the printing trade, it has been customary for years to use the 
names "red," "green," and "blue" for the colors of the taking filters, 
but to speak of the corresponding subtractive printing colors as 
"blue," "red," and "yellow." These latter names are, of course, 
poorly chosen, and have caused no end of confusion. The motion pic- 
ture industry will do well to head off similar confusion by adopting 
different names for the subtractive components. It would be logical 
and reasonable to speak of these subtractive printing colors as "minus- 
red," "minus-green," and "minus-blue." Such terms are objection- 
able both because of their length and their negative nature. The 
names "magenta" and "cyan" have been proposed in place of "minus- 
green" and "minus-red," respectively. Retaining the name "yellow" 
for the "minus-blue" component, the three subtractive components 
become "cyan," "magenta," and "yellow," corresponding respec- 
tively to the red, green, and blue taking filters. Magenta is very 
well established as the name of a definite color, and there is no ques- 
tion about its suitability. "Cyan," as a name, has not been so 
well established; but no more suitable name has been suggested. 
It is widely used in the aniline dye industry, is short, and is described 
in Webster's dictionary as "a hue between green and blue." The 
Committee, therefore, recommends the general adoption of the 
word "cyan." 

A number of multi-layer color processes have been proposed; 
several of them have been worked on; and certain of them are in 
commercial use. The terms used in this field are in need of clarifica- 
tion. The word "bi-pack" is understood to mean two films placed in 
contact, generally face to face, and a "tri-pack" is understood to mean 
three films in a "sandwich" arrangement. In the usual bi-pack, or tri- 
pack, the individual films or layers of emulsion are readily separable. 
In contrast with these, the word "monopack" has been used to indi- 
cate an arrangement in which several layers are integrally joined to- 

*Presented at the Spring, 1936, Meeting at Chicago, 111. 
164 



COLOR COMMITTEE 165 

gether in manufacture so as to be physically inseparable. This term 
is generally regarded as inadequately descriptive; rather the adjec- 
tive "integral" should be used, as an "integral bi-pack" or an "inte- 
gral tri-pack," to describe two or three layers that are not physically 
separable. 

The new Kodachrome process, which, according to the above-given 
definition makes use of an integral tri-pack, is the first commerciali- 
zation of a process coming under a classification described by Wall 2 
as "developed color." It is more accurate to speak of "color develop- 
ers" and "color developer processes" and, therefore, the use of these 
latter phrases is recommended. 

The Gasparcolor process is of the type characterized by the fact 
that a dye distributed uniformly in the emulsion layer is selectively 
discharged under the control of a silver image. For processes of this 
kind the name "catalytic bleach"' is sometimes used, but the preferred 
and recommended term is "selective dye bleach." 

Dr. Forsythe, Director of Research of the General Electric Co., at 
Nela Park, has recommended a revised definition of "effective wave- 
length" and of "black body." 

The Color Committee would. like also to recommend to, and im- 
press upon, the Society the great importance of establishing more uni- 
form conditions in respect to viewing-screens throughout the indus- 
try. This matter is important enough in black-and-white projection, 
but is even more important in the projection of natural color pictures. 
The whole matter has been difficult from a practical point of view in 
the past years because of the widespread use of radically different 
types of light-sources. The tendency in theaters today is strongly in 
the direction of arc lights of high intensity and high color- temperature. 
This Committee, therefore, urges the Society to study the findings of 
the Projection Screen Brightness Committee and to set up a standard 
of screen brightness for the industry. This important work should be 
vigorously publicized, and the superior quality to be achieved by ad- 
hering to such a standard brought vigorously to the attention of pro- 
ducers and exhibitors. Supplementing the standard of screen bril- 
liance, a specification of the most desirable spectral quality of the pro- 
jection light should be established from the point of view of good color 
rendition. 

J. A. BALL, Chairman 

W. H. CARSON C. H. DUNNING H. W. MOYSE 

O. O. CECCARINI R. M. EVANS A. WARMISHAM 

A. M. GUNDELFINGER 



166 COLOR COMMITTEE [j. S. M. p. E. 

REFERENCES 

1 "A Glossary of Color Photography," /. Soc. Mot. Pict. Eng., XXIV (May, 
1935), No. 5, p. 432. 

2 WALL, E. J. : "History of Three-Color Photography." Amer. Phot. Pub. Co. 
(Boston), 1925. 



SUPPLEMENTARY GLOSSARY OF COLOR PHOTOGRAPHY 

Beam Splitter, or Fractional Light Diverter An optical system so 
arranged as to reflect and transmit portions of a light-beam 
along different optical axes. 

Black Body 1. A body which when heated radiates ideally ac- 
cording to fundamental physical laws (i. e., Planck's radiation 
law) relating energy, frequency, and absolute temperature. 
The properties of incandescent tungsten or carbon approximate 
those of a black body. 2. A body which absorbs all light inci- 
dent upon it. 

Bleach 1. (v.t.) To make white or whiter, by a chemical process 
or by exposure to intense radiation; 2. in photography, to re- 
move, or to convert to a compound, by chemical action (usually 
oxidation) the silver of an image. 3. (n.) a chemical reagent 
used for bleaching. 

Bleeding of Color The diffusing of dye or metallic tone away from 
an image. 

Carbro A process in which the differential insolubilization of the 
carbon tissue is produced by chemical reaction between the 
bromide print and the tissue. 

Cinecolor A subtractive two-color process. Prints are made on 
double-coated or single-coated film, from either bipack or any 
color-separation negative. 

Chromatone A color printing process which requires superimposing 
three collodion-gelatin layers whose images have been bleached 
and toned to the three subtractive colors. 

Dufaycolor A regular mosaic or reseau screen-film process for 
three-colored additive cinematography by either direct reversal 
or negative and positive technic. 

Effective Wavelength The effective wavelength of a screen is the 
wavelength that it is necessary to use in the radiation laws in 
order to calculate a ratio of radiation intensities equal to the 
ratio of the luminosities measured when one observes a black 
body through the screen at the two different temperatures. 



Aug., 1936] COLOR COMMITTEE 167 

Kodachrome A color process brought out in 1935, for 16-mm. 
film, which uses an integral tri-pack developed by a reversal 
process involving color developers', whereby a subtractive posi- 
tive original is produced. 

Reseau A geometric mosaic on photographic film, for the produc- 
tion of natural color-film. 

Schultz Number A number given to a dyestuff in the "Farbstoff- 

tabellen" of Schultz and Lehman, published by Akademische 

Verlagsgesellschaft, of Leipzig. (It should be noted that the 

numbers in the seventh edition (1931) are different from those 

in the previous six editions.) 

Selective Dye Bleach A process wherein a dye distributed uni- 
formly in the emulsion layer is selectively discharged under the 
control of a photographic image. 

Subtractive Primaries The three printing colors used in a three- 
color subtractive process : magenta (minus-green), cyan (minus- 
red), and yellow (minus-blue). 



IMPROVED RESOLUTION IN SOUND RECORDING AND 
PRINTING BY THE USE OF ULTRAVIOLET LIGHT* 

G. L. DIMMICK** 

Summary. The resolution of sound-film records has been increased by the use 
of ultraviolet light in recording and printing. Because of the absorption charac- 
teristics of the emulsion, exposures made by ultraviolet light are restricted to the 
surface. This reduces spreading of the image. The fogging of the track that usually 
results from halation and reflection from objects in the path of the light is almost en- 
tirely eliminated. Since the light-energy is restricted by means of a filter to a very 
narrow band, chromatic aberration of the lenses is reduced. 

The definition of the very fine recording light-beam is limited by diffraction. This 
limitation is materially decreased as a result of the decrease in wavelength of the radiant 
energy. 

It is the object of this paper to discuss improvements in the resolu- 
tion of photographic sound-film records by the use of ultraviolet light 
in printing and recording, and to point out the nature and magnitude 
of the resulting improvements in sound-record characteristics. The 
idea is not new, having been proposed previously by Oswald and 
others, but this is, to our best knowledge, the first practical applica- 
tion. 

It will be instructive first to consider the nature of an ideal photo- 
graphic sound recording system, and although the variable-width 
system is discussed here because the present improvements have been 
made in connection with the development of variable-width recording 
methods, the requirements of the variable-density system are very 
similar. Ideally, the photographic recording of sound is accomplished 
by imaging a uniform line of light, of infinitesimal width and of length 
varying with time, upon a uniformly moving photographic medium 
which develops black where, and only where, it has been exposed to 
the line of light. 

While it is easy for the mind to conceive these ideal conditions, the 
real recordings must be made with physical apparatus upon a physical 

*Presented at the Spring, 1936, Meeting at Chicago, 111. 
**RCA Manufacturing Co., Inc., Camden, N. J. 
168 



ULTRAVIOLET LIGHT IN RECORDING AND PRI NTING 169 

medium, so that the real accomplishment of the result is beset with 
many difficulties and is brought about slowly through an extended 
process of development or growth. 

The nature of the requirements of an ideal recording system clearly 
suggests that the whole matter is one of resolving power in the appara- 
tus and of resolving power in the medium ; that is to say, we must seek 
a means of producing an image of a slit that is of infinitesimal or ex- 
treme narrowness, which can be accomplished only by an optical 
system of high resolving power. Furthermore, we must have a me- 
dium that will record an impression of this image with perfect fidelity, 



Bos* 




FIG. 1. 



Path of the recording light-beam through the emulsion and 
base of the film. 



which means that the medium must also have a very high resolving 
power. 

Continuous development of the variable-width recording system 
over a period of years had brought optical recording systems to such 
a state of perfection that, despite improvements in sound recording 
emulsions, very little improvement in record quality resulted from 
further increases in optical resolving power. This meant that the 
limit of record quality was set by the resolving power of the photo- 
graphic emulsion, and that further improvements had to be sought 
in the direction of increasing this resolving power. 

It had long been known that some day no further improvements 
would be possible without increased film resolution, but possibilities 



170 G. L. DlMMICK [J. S. M. P. E. 

of improvement in other directions continued to offer themselves for 
many years and were of sufficient importance to keep the matter of 
film resolution still in the background. Recently, methods of im- 
proving film resolution have received more serious consideration, and 
it is the solution of this problem that is the subject of this paper. 

Let us consider first what occurs in the emulsion when recording in 
the conventional manner. The image of the recording slit has al- 
ready been decreased in width .to one-sixth of one mil to reduce the 
slit effect at high frequencies, but since the emulsion thickness is one- 




Wavelenctb (Angstrom Units) 

FIG. 2. (A) Transmission characteristic of recording filter; (B) 
transmission characteristic of emulsion; (C) sensitivity characteristic 
of commercial sound recording. 

half mil, and the emulsion itself is a white translucent diffusing mate- 
rial, it is impossible to restrict the light within the emulsion to the 
dimensions of this slit image. The reason for this is made clear in 
Fig. 1, which shows a cross-section of the film and the recording light- 
beam drawn to scale. After the light enters the top layer of the film, 
it is immediately scattered, and exposes much of the silver outside 
the outlines of the light-beam. The intensity of the light-beam de- 
creases as it penetrates the emulsion, because of absorption, but it 
still has considerable actinic value upon reaching the base of the film. 
Part of the light is then reflected back from the base, exposing the 
bottom side of the emulsion. Of the light that strikes the base at 



Aug., 1936] ULTRAVIOLET LIGHT IN RECORDING AND PRINTING 171 

less than the critical angle, only a small part is reflected; but the part 
that falls outside the critical angle suffers complete reflection, giving 
rise to halation. The light that is transmitted through the base must 
be completely absorbed by painting all the surfaces that it strikes, or 
the stray light will be increased by reflection from these surfaces. 

All these objectionable sources of stray light can be eliminated and 
the resolution of the film greatly improved by restricting the luminous 
energy to a small band of frequencies that are strongly absorbed by 
the emulsion. This is accomplished by inserting a filter in the path 
of the light from the incandescent recording lamp or printing lamp, 




Wavelength (Angstrom Units) 

FIG. 3. Curves of relative energy from incandescent tungsten at 
various temperatures. 



as the case may be. Curve A , Fig. 2, shows such a filter, transmitting 
freely in the band 3400 to 3950 A. Curve C shows how the sensi- 
tivity of a commercial sound recording film varies with the wave- 
length. This is not a true film sensitivity curve, but shows the prod- 
uct of the energy from the incandescent lamp and the film sensitivity 
at any wavelength. It may be seen that energy of wavelengths from 
3200 to 5200 A. contributes materially to the resultant exposure. 
Curve B shows the transmission of the emulsion, and was obtained by 
placing two pieces of film with their emulsions in contact and expos- 
ing one through the other. It is interesting to note that the emul- 
sion transmits very freely light of wavelengths longer than 4300 A, 
but absorbs heavily at wavelengths less than 4000 A. By restricting 



172 



G. L. DlMMICK 



[J. S. M. P. E. 



the luminous energy to the small band of curve A, the emulsion be- 
comes a strong absorption filter for all the light falling upon it, and 
two important results are accomplished. First, the exposure of the 
emulsion is restricted to the surface, because the energy is absorbed 
before it can penetrate very far; and, second, practically no energy 
passes through the emulsion, to be reflected and cause stray light. 
The first result is probably the more important. It is obvious that if 
it were possible to expose an extremely thin layer and obtain sufficient 
density, the resolution would be improved because there would be 
very little spreading of the image. For variable-width sound record- 
ing, it is necessary that the emulsion be sufficiently thick to produce a 
density of at least 1.5 when all the silver is exposed. Ordinary posi- 




Transmission Characteristics of Olr.su 
2 Millimeters Thick 



Corninc To. 970 - Core* D 

Chemioal Pyrex and B &. L ipeitacle Class 

Soda Lime Glass 

Lead Lime Glass 

Borosilioate Glass 



elength (Uicro.is) 

I I I I I I I I 



I I I I 



FIG. 4. Transmission characteristics of various types of glass, 2 millimeters 

thick. 



tive emulsions have about three times this much silver, which excess 
serves to increase the speed and contrast at the expense of resolution. 
When a photographic emulsion is required to reproduce variations in 
brightness faithfully, as in the case of photography and variable- 
density sound recording, the proper contrast is most important; but 
for variable-width sound recording, contrast is relatively unimportant 
except so far as it improves the resolution. 

The use of a restricted frequency band not only increases film reso- 
lution, as explained, but also improves the resolving power of the opti- 
cal system, and consequently the definition of the image of the slit. 
This improvement is of a dual nature; first, losses in definition due to 
chromatic aberration are reduced by using a narrow band of radia- 
tions, and, second, the use of the short ultraviolet wavelengths re- 
duces diffraction at the slit and improves optical resolving power. It 



Aug., 1936] ULTRAVIOLET LIGHT IN RECORDING AND PRINTING 173 

is well known that the resolving power of optical systems can be im- 
proved by shortening the wavelength of the light with which the ob- 
ject is illuminated, and important advances in microscope practice 
have been based upon this principle. Although in recording sound 
our optical system is the reverse of a microscope, producing a reduced 
image of a large object, its resolving power, and consequently image 
definition, depend in the same manner upon wavelength. 

The narrow frequency band between 3400 and 3950 A is ideally 
suited for sound recording, because radiations of this frequency can 



Recorded and Printed 
Without Filter 



Print Density 1.2 




Recorded and Printed 
With Filter 

Print Density 1.2 




1000-cycle peak 



/Z /.* /.* 

Negative Density 



/& 



Negative Density 

FIG. 5. Over-all effect of the ultraviolet method of recording and printing. 



be obtained from an incandescent lamp and because ordinary flint 
glass, which is necessarily used in the corrected lenses, transmits this 
band. In other words, this band of wavelengths is attainable from 
an ordinary light-source, and can be transmitted through an ordinary 
optical system. Fig. 3 shows curves of the relative energy from in- 
candescent tungsten at 3500, 3300, and 3000K. The energy in- 
creases rapidly as the wavelength or the temperature is increased. 
Among other things, the life of an incandescent filament is a function 
of its temperature and the ratio of the surface area to the volume of 
the filament. A satisfactory compromise of lamp life and luminous 



174 G. L. DIMMICK [J. S. M. P. E. 

efficiency in the band 3400 to 3950 A has been found in a lamp having 
a current rating of approximately 7 l /z amperes. 

The curves of Fig. 4 show the transmission of various types of glass 
having a thickness of 2 millimeters. The two achromatic lenses used 
in the recording optical system have a total of about 5 millimeters of 
flint glass. The condenser lenses are made of spectacle crown glass, 
which has much higher transmission at short wavelengths than flint 
glass. 

The over-all effect of the improved method of recording and print- 





White Light Ultraviolet 

FIG. 6. Enlargements of sound records of 9000-cycle prints: (left} 
made with white light, (right) with ultraviolet light. 

ing is shown in Fig. 5. The peak and valley transmissions of a 1000- 
cycle and a 9000-cycle print are plotted against negative density. 
The curves at the left show the effect of recording and printing with 
white light. Those on the right show the improved effect of record- 
ing and printing with ultraviolet light. The shaded portion repre- 
sents the relative attenuation at 9000 cycles. It will be observed 
that the maximum response at 9000 cycles for white light is 55 per 
cent, and for ultraviolet light 78 per cent of the 1000-cycle value. 

Attenuation of high frequencies is not the only manifestation of low 
resolution in sound records. Such attentuation arises from too little 
transmission through the print valleys, and too high transmission 



Aug. , 1936 ] ULTRAVIOLET LIGHT IN RECORDING AND PRINTING 1 75 



through the print peaks. It is easily seen that if the excess of trans- 
mission through the peaks is not equal to the deficiency of transmis- 
sion through the valleys, then at any given frequency the average 
transmission of the sound-track will not be equal to 50 per cent, and 
will be a function of the amplitude of the recorded wave. When this 
unbalanced condition occurs, sounds consisting of high frequencies 
whose amplitude varies at a lower frequency can not be reproduced 
without also reproducing the frequency of the amplitude variation. 
This gives rise to a spurious sound, which did not originally exist at 




Screen 

FIG. 7. Schematic diagram of Photophone recording 
optical system. 



all and is especially noticeable in the sibilants and in metallic sounds 
such as the jingling of keys. Control of this effect and its complete 
elimination are achieved by properly balancing conditions of exposure 
and development. It can be seen that the peak and valley attenua- 
tions are equal over a much wider range of negative density in the case 
of ultraviolet recording and printing than in the case of white light 
recording and printing. Thus, the use of ultraviolet light increases 
the flexibility of the system which, in practice, is important because 
it relieves the demands upon the film processing laboratories. 

Fig. 6 shows an enlarged view of a 9000-cycle print. A was made 
with white light for both the negative and print, and B was made with 
ultraviolet light for both negative and print. 



176 G. L. DIMMICK [J. S. M. P. E. 

Fig. 7 presents a schematic diagram of a Photophone recording 
optical system. 1 For recording with ultraviolet light, the ultraviolet 
filter is placed between the lamp a and the condenser b, to filter the 
light that passes through the recording aperture c. A red filter is 
placed before the monitoring aperture i so that the image upon the 
monitoring screen will be visible to the eye while at the same time the 
monitoring system can introduce no actinic stray light into the re- 
corder. The objective that images the slit upon the film is achroma- 
tized for 3650 A in the ultraviolet, and for the mercury green line so 
that the slit may be focused upon the film by removing the ultra- 
violet filter and observing the image through a Wratten series 62 
mercury green filter. 

The recordings that were demonstrated were noiseless push-pull 
ultraviolet recordings, printed with ultraviolet light on the RCA non- 
slip contact printer. 2 An experience in the production of the selec- 
tions from The Eternal Road demonstrated the importance of printing 
high-quality recordings with a non-slip printer. The first prints were 
made on a commercial contact printer especially adapted to sound 
printing, and with ultraviolet light. The result was not acceptable 
to the composer or his colleagues. The non-slip printer was then ob- 
tained, and prints were made with it that were pronounced satisfac- 
tory by these persons, who, it goes without saying, are extremely 
critical judges. 

REFERENCES 

1 SACHTLEBEN, L. T.: "Characteristics of Photophone Light Modulating 
System," J. Soc. Mot. Pict. Eng., XXV (Aug., 1935), No. 2, p. 175. 

2 BATSEL, C. N.: "A Non-Slip Sound Printer," /. Soc. Mot. Pict. Eng., XXIII 
(Aug., 1934), No. 2, p. 100. 

DISCUSSION 

MR. FRANK, JR.: In order that you may understand the conditions under 
which the demonstration was given, the music was recorded as music for a legiti- 
mate stage production. The recording is supposed to take the place of the cus- 
tomary orchestra. No photograph, of course, was made of the orchestra when the 
record was made. You are supposed to experience the illusion of having the or- 
chestra in the same auditorium with the production. 

MR. WOLF: The question was raised, Mr. Batsel, as to the difference between 
the variable-width and variable-density recordings by this method. 

MR. BATSEL: In Fig. 6, showing a variable- width sound-track, the light and 
dark areas are sharply defined. Usually there is a gradation in density, rather 
than sharp black and sharp white. 

MR. RICHARDSON: Which type of recording is affected most by using the ultra- 
violet method? 



Aug., 1936] ULTRAVIOLET LIGHT IN RECORDING AND PRINTING 177 

MR. BATSEL: I should say that the effect is greatest in variable-width record- 
ing, because that type of recording depends upon image definition. 

MR. JOY: What was the wattage of the light-source used? Is there any diffi- 
culty in getting the necessary amount of light through these niters? 

MR. BATSEL: With a Ve-niil s lit, we get a density of 1.8 on the negative through 
the filter, with our ordinary optical system, using a 10-volt, 7.5-ampere lamp. 
The filter was a Corning 584 ultraviolet filter. 

MR. TASKER: Was the lamp current exactly 7.5? 

MR. BATSEL: About 8. 

MR. TASKER: What was the temperature? 

MR. BATSEL: About 2100 A. 

MR. ROBERTS: As I understand it, you choose a band of wavelengths that are 
absorbed by the emulsion. Is the absorption a characteristic of the undeveloped 
film with high silver highlights or of the gelatin itself? Is it not a fact that if it 
were a characteristic of the gelatin you would not get enough light through to the 
print? 

MR. BATSEL : It is a characteristic of the raw emulsion. 

MR. WOLF: What proportion of the improvement in this recording is due to the 
printing and what due to the ultraviolet recording method? 

MR. BATSEL : The improvement is due, as stated in the paper, to the fact that 
the light does not penetrate into the emulsion. The light in the band we are using 
is absorbed readily ; the film is naturally a filter in itself. 

MR. WOLF: The prints were not satisfactory before you improved the printer? 

MR. BATSEL: No. Sprocket modulation, slippage, bad contacts, and things 
of that sort, put distortion into the print that was not in the negative. Referring 
to Fig. 6, the valleys would be filled in and the peaks wiped out, but not in a uni- 
form manner. Consequently, there was distortion. 

MR. WOLF: Do you regard the non-slip printer as really quite an improvement 
in the printing process? Could it be used for other types of film as well as for 
ultraviolet recorded film? 

MR. BATSEL: Yes; for printing any sound-track. 

MR. FRANK, JR. : It was recently announced at Hollywood, in connection with 
the non-slip printer, that anyone who is interested in manufacturing a non-slip 
printer using the RCA design features and patents can obtain a license to do so if 
he will communicate with us in Camden; and licenses so granted will not involve 
cost to the licensee. 

MR. RICHARDSON: Would the affect of the ultraviolet light upon the film as- 
sure permanency at least equal to that attained now with white light? In other 
words, would the effect upon the silver possibly be as lasting as it is now, or more 
or less that is, with equal care in fixing and washing? 

MR. DEPUE: I have in my possession a film made in 1897. I washed it and de- 
veloped it myself, and of course it was washed very thoroughly. That film today, 
so far as I can see, has not lost anything in quality. Perhaps it has a few specks 
in it, but to all intents and purposes, the film is exactly in the same condition 
it was in when I developed it in 1897 a black-and-white film, made outdoors. 
We did not have artificial light then. It is a 60-mm. film. 

MR. MILI: The photographic deposit of silver in the case of recording sound 
with ultraviolet light is essentially a surface deposit, whereas in the case of re- 



178 G. L. DIMMICK 

cording with white light it is a deposit of appreciable thickness, penetrating below 
the surface. If atmospheric conditions affect the film it is obvious that most of 
the change will occur at the surface, and that the sound-track obtained with 
ultraviolet light will suffer more than that obtained with white light. Again, any 
mechanical injury, such as scratching, would be more detrimental to the former 
than to the latter. 

MR. KELLOGG:* Although a number of expressions of opinion have been given 
on the question whether films recorded by ultraviolet light might prove less per- 
manent than those recorded by white light, and these opinions were all to the 
effect that such a danger was extremely remote, those who might have been in a 
position to speak with most authority were not at the meeting at the time. I feel 
that it will be desirable to offer enough further evidence to allay any fears of 
such a danger. 

After the meeting I spoke to a number of members of the Society who are ex- 
ceptionally well informed upon photographic materials. Without exception, 
they felt that such a danger was practically unthinkable. In the first place, the 
exposure to ultraviolet light in recording, which produces the image, is infinitesi- 
mal compared to the exposure to ultraviolet light to which practically all films are 
subjected in handling subsequently to development. Therefore, any such lack 
of permanence would have to be the result of some effect to which the film was 
susceptible prior to processing, and not subsequently. It is well known that pro- 
longed exposure to ultraviolet light will cause film base to deteriorate, but the dos- 
age of ultraviolet required to accomplish that is thousands or perhaps millions of 
times the dosage used in exposing the emulsion. The best evidence would be to 
examine spectrograms in which portions of the image are produced by ultraviolet 
and portions by white light. 

Among others I talked to Dr. L. A. Jones, who was willing to be quoted as say- 
ing that no one need have the least misgivings as to the permanence of negatives 
made with ultraviolet light as compared with those made with visible light. He 
recalled spectrograms made years ago which are still in good condition. 

* Communicated. 



PRIMARY CONSIDERATIONS IN THE DESIGN AND 
PRODUCTION OF THEATER AMPLIFIERS* 



T. D. CUNNINGHAM** 

Summary. Certain considerations in the design and production of theater ampli- 
fiers are of primary importance to the reliability and performance of the equipment 
in service^ These comprise, in general, the choice of the component parts; the ar- 
rangement of the parts in the complete assembly; the construction of pre-production 
models for proving the design; and the care in the manufacture and final test of the 
product. 

Early types of theater amplifiers were for the most part designed 
and produced with limited knowledge of actual field operating condi- 
tions the natural consequence of the birth of a new industry and 
the immediate need of that industry for amplifying equipment to 
fulfill its requirements. Besides the disadvantage of battery or 
motor-generator operation, the amplifiers were large and in some 
respects rather complicated to install and operate, owing to the fact 
that they were elaborately equipped with numerous meters, switches, 
and other controls. Nevertheless, looking back upon the performance 
of those amplifiers, we are forced to admit that for the greater part 
they did their job well, particularly when we consider the fact that 
they were produced on short notice for a new industry. 

With the advent of complete a-c. operation, and with the increased 
knowledge of practical field operating conditions, the designs of 
sound motion picture amplifiers became somewhat simpler, with 
regard to installation and operation. Today the industry requires 
equipment that can be installed upon short notice and with a mini- 
mum of effort, and which embodies only the control features essential 
to proper operation. More important than that, the industry de- 
mands equipment that will perform to the complete satisfaction of 
the patrons, and will continue so to perform throughout its life with 
a minimum number of interruptions. With these requirements in 
view, in this paper will be outlined the primary considerations that 

* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** RCA Manufacturing Co., Camden, N. J. 

179 



180 T. D. CUNNINGHAM [j. s. M. p. E. 

must be taken into account in the design and production of present- 
day theater amplifying equipment. 

The first requirement in the design of a theater amplifier is a 
knowledge of the size and the general character of the theaters which 
it is to serve. From experience gained in the field, four general types 
or sizes of equipment have been found sufficient to serve the majority 
of the theaters, not only from the point of view of performance, but 
economy as well. 

Practical methods have been established for predetermining the 
audio power required to attain good sound distribution with loud 
speakers of known characteristics, in auditoriums corresponding to 
the four general sizes of equipment. Experience in the field and in the 
laboratory has made it possible to know in advance the general effects 
of specific types of theaters upon the response of the system and the 
latitude of variation that must be allowed to compensate for those 
effects. To adapt the sound system more closely to varying types of 
theaters and films, the reproducing amplifier should be provided with 
means for regulating its frequency response to conform to the existing 
circumstances. 

Knowing the power required for the loud speakers and the power 
delivered by the sound head with the average run of films, the de- 
signer is in a position to calculate the total amplification (including 
a reserve for compensating for varying modulation levels from film to 
film) required to realize the required output power. Many types of 
vacuum tubes are available for the amplifier circuits, each with its 
particular operating characteristics. The existence of so many types 
simplifies somewhat the problem for the design engineer; neverthe- 
less, care and judgment must be used in selecting the type or types 
to be applied, in view of the requirements to be met in the design and 
operation of the equipment, and such factors as replacement cost, 
ease of obtaining replacement parts, and performance suitability 
must be considered. Characteristics such as freedom from micro- 
phonics, filament power consumption, and ability to produce the 
required gain or power output with minimum harmonic distortion 
are the bases of selection for performance suitability. 

The lay-out of the circuit and determination of its constants 
follows the selection of the tubes. For the most part, the determina- 
tion of the circuit constants, to provide the requisite amplification, 
frequency response, and audio output, is accomplished mathemati- 
cally. Although such calculations may often be quite accurate, it is 



Aug., 1936] DESIGN AND PRODUCTION OF AMPLIFIERS 181 

always regarded good practice to check the circuit constants by means 
of a rough set-up in the laboratory. This procedure not only en- 
ables a preliminary check on the circuit operation, but in some in- 
stances uncovers undesirable features and suggests improvements. 

No factor is more important in the design of theater amplifiers 
than that of selecting the principal component parts : transformers, 
reactors, capacitors, resistors, volume controls, switches, relays, etc. 
First of all the designer must have a knowledge of the conditions under 
which the equipment is to operate. He must know (1) whether or 
not the equipment is to be exploited in domestic, foreign, or both 
fields, and the extremes of temperature and humidity normally 
encountered in those areas; (2) the extreme daily cycle of operation 
to be anticipated; and (3) the type and variation of power supplied 
to operate the equipment. In addition, he must make proper allow- 
ance in his design for maximum working voltages and temperature 
rises. Since most sound equipment produced is subject to installation 
in either domestic or foreign fields, the component parts should be 
designed to operate reliably at a temperature at least 45 C below 
ambient temperature, and a relative humidity of at least 90 per cent. 
Further, the parts must be designed to operate without failure for 
approximately 15 hours daily for several years, even though on the 
average the cycle of operation is appreciably less than that. In order 
to assure such reliable operation, high factors of safety must neces- 
sarily be allowed. In designing capacitors and transformers, in 
particular, although this applies equally well to other components, 
an accurate knowledge of the working voltages is necessary so that 
sufficient insulation may be provided against possible breakdowns. 
In the design of such parts as relays, volume controls, and switches, 
careful consideration must be given to the choice of the contact 
material and the action of the contacts, to assure quiet operation, 
particularly in high-amplification circuits. Assurance of the reliability 
of most of the parts may and should always be gained through life- 
tests in the laboratory, which may take the form of continuous 
application of abnormal voltages for many weeks to capacitors, 
transformers, and resistors; or the operation of switches, volume 
controls, and relays for many thousands of cycles or rotations under 
abnormal temperature and humidity, to simulate long periods of 
service. 

Of primary importance in the assembly design of theater amplifiers 
is the consideration of mechanical strength and the possibility of 



182 T. D. CUNNINGHAM [j. S. M. p. E. 

transporting the device to its destination without damage. No less 
important is the matter of the placement of the components with 
respect to each other to assure satisfactory electrical performance. 
This consideration is particularly important in a-c. operated ampli- 
fiers, which for the most part constitute present-day designs. The 
principal undesirable characteristics to be guarded against are (a) 
background noise, including hum, (b) microphonics, and (c) in- 
stability, in the form of regeneration or oscillation. The main 
sources of hum in an amplifier are the power transformer, the filter 
reactor, and the main filter capacitor, owing to the fields set up in and 
about them as a result of the high alternating components of the 
currents in them. Therefore to minimize the effects of these parts 
upon the rest of the circuit, the power transformer and the filter 
reactor in particular should be well shielded magnetically, and placed 
as far as possible from the input and interstage circuit components. 
Further advantage has been found in orienting the cores and coils 
of the transformers and reactor units so that their magnetic coupling 
with the audio input and interstage transformers is weakest. To 
reduce the hum further, the audio input and interstage transformers 
must be effectively magnetically shielded. As mentioned before, 
under the subject of tube selection, a low microphonic propensity 
is an important factor. In addition, however, further protection 
against microphonics must be provided by very flexibly cushioning 
at least the first two audio tube stages. The most effective cushioning 
is provided by sponge rubber or light steel spring mountings. The 
designer can do much to assure stability of operation by being careful 
to keep the input and output circuits as widely separated as possible. 
So far as practicable, that can best be done by placing the input and 
output terminal boards and wiring at opposite ends of the amplifier. 

The design engineer is today giving the installation and service 
engineer and the projectionist more and more consideration in respect 
to the lay-out and design of theater equipment. More specifically, 
he has in mind to do everything practicable in the design to make it 
easier to install, operate, and service the equipment. 

(a) Installation Considerations. A theater amplifier, whether de- 
signed for rack or wall mounting, must be as small in size and light 
in weight consistent with good performance, in order that it may be 
handled as easily as possible during installation, and occupy an 
unobjectionable amount of space in the projection room. It has been 
found that the front-service type of rack or cabinet is mot 



Aug., 1936] DESIGN AND PRODUCTION OF AMPLIFIERS 183 

cal of space since it can be mounted directly against the wall of the 
projection room without the necessity of gaining access at the rear. 
Much advantage can be gained in selecting the size and number of 
conduit knockouts, and particularly their location, so as to permit 
making the installation with a minimum expenditure of labor and 
time. Provision should be readily available for adjusting the equip- 
ment to the nominal power supply voltage and to the frequency re- 
sponse characteristic most suitable to the theater. 

(b) Operation Considerations. The projectionist is quite occupied 
in most instances, in keeping the show going, and it is not fair to 
burden him with a number of unessential controls, the adjustment of 
which he must continually keep in mind. With that in mind, the 
designer has in recent years greatly simplified and reduced the number 
of controls on amplifier panels. To some persons, the older designs 
adorned with many meters and controls of various kinds seem to be 
impressive, but the important consideration in equipment of this 
nature is that it shall be simple to operate and permit the least chance 
of error upon the part of the operator. From that point of view it 
has been found desirable and convenient to be able to control the 
volume from a point in the auditorium as well as in the projection 
room. An attendant in the auditorium is, by virtue of his location, 
better able to judge the level of the sound, and to adjust it properly 
to the prevailing conditions. For that reason therefore, provision 
should be made in designing the equipment for the installation of a 
satisfactory remote volume control. The capacitor motor type with 
a control station in the auditorium has been found to perform quite 
satisfactorily in this respect. 

(c) Service Considerations. It may be safely said that no equip- 
ment has yet been made that had no operating difficulties, even though 
the greatest of care may have been exercised in designing and producing 
it. Notwithstanding the fact, the designer and producer of equipment 
must continue his efforts toward the realization of trouble-free opera- 
tion. Until that goal has been attained, the service engineer and his 
problems must be given due consideration in the design and produc- 
tion of the equipment. In addition to his regular calls, the service 
engineer is subject to emergency calls, in view of which, particularly, 
the designer should give all consideration to the need of locating and 
correcting troubles in a minimum of time and with least effort. 
There must be constant appreciation of the service problem during 
the process of design, with particular reference to (1) the accessibility 



184 



T. D. CUNNINGHAM 



[J. S. M. p. E, 




Aug., 1936] DESIGN AND PRODUCTION OF AMPLIFIERS 185 

of the parts; (2) the identification of the parts; (3) the judicious 
segregation of the parts most likely to give difficulty; and (4) the 
proper fusing of important branches of the circuit. 

Without doubt the most important of these considerations is that 
of accessibility of the parts. The front-service form of construction 
obviously lends itself quite readily to servicing. The panel is mounted 
close to the wall, and there is no necessity of getting at the rear of it; 
as the result, the service engineer has ample space in which to work. 
Next is the matter of accessibility of the various sections of the panel 
and the component parts in those sections. A form of construction 
that has proved to be quite satisfactory from this pcint of view is 
shown in Fig. 1. Each amplifier comprises three principal parts; 
namely, a vertical panel, a base support, and a base proper. Upon 
the vertical panel are mounted the heavy power supply parts, such 
as the power transformers, filter reactors and capacitors, etc. Upon 
the base support are mounted a few parts, but its main function is 
that of supporting the main base and some of the inter-cabling. The 
main base supports most of the amplifier parts proper. When the 
amplifier is completely opened for inspection or service by means 
of the supporting hinges, a large majority of the parts and their 
connections are open to inspection or removal if necessary. The main 
amplifier base can be easily removed without the use of a soldering 
iron, and replaced or worked upon by itself. In its operating position, 
the base is folded back into the rack, and a perforated cover, fastened 
by easily removable thumb-screws, holds it in place as shown. 

The component parts may, and preferably should, be marked so as 
to enable the service engineer to identify them readily. Parts such as 
capacitors, which are somewhat critical as to failure, should be kept 
segregated as much as possible from other components such as trans- 
formers and reactors. In portions of the circuit employing rather 
large capacitances, it is well to split the capacitances into several 
sections in parallel, so that if one section fails it can be quickly cut 
out of service with least interruption to the program. Important 
portions of the circuit should be fused against possible trouble. This 
applies not only to the primary circuit, but to some parts of the 
secondary circuits as well. For example, it is deemed wise to fuse the 
separate filter capacitor sections so that in the event of failure of a 
section the program may be permitted to continue until the end, 
when repairs can be suitably made. 

Another consideration that must be constantly kept in mind during 



186 T. D. CUNNINGHAM [J. S. M. p. E. 

the design of a theater amplifier is the fact that it must conform to 
the requirements of the National Board of Fire Underwriters. This 
is desirable, for several reasons: it is a form of insurance against 
damage by fire to either the equipment itself or its surroundings; 
it insures against unnecessary hazards to the lives of those working 
with the equipment; and adherence to the code of the Underwriters 
conduces to greater uniformity among the regulations of the munici- 
palities of the country. In some respects, complete compliance with 
these regulations makes the job of the designer more difficult; but 
in the end, the effort expended is well worth while. Most important 
among the requirements are the use of materials throughout which 
will withstand the temperatures encountered in apparatus of this 
kind, the proper insulation of all current-carrying parts, and the pro- 
tection of all primary and high secondary voltages against accidental 
contact. 

The design completed, pre-production models should logically be 
made from the engineering drawings: (1) to establish definitely in 
the laboratory whether the device as designed fulfills its performance 
requirements; (2) to check the accuracy of the dimensions specified 
on the drawings; (3) to establish test limits for subsequent production 
units; and (4) to make available units for field tests, to assure suit- 
ability of performance and mechanical construction. 

With the assurance of suitability of performance and mechanical 
construction, the engineering drawings may be released for quantity 
production. Particular care must be exercised by the inspectors in 
the Production Department to insure that all parts of the amplifier 
are produced in strict accordance with the engineering drawings, 
and that the permissible variations and tolerances are adhered to. 
Parts both made within the factory and purchased outside must be 
individually inspected and tested to determine proper compliance 
with the specifications before they are assembled into the amplifier. 
After completion of the assembly, the amplifier is ready for the final 
inspection and test. All mechanical points, including the inter- wiring 
of component parts, should be thoroughly inspected, and if not cor- 
rected should be made so before the beginning of final test. Final 
test of a theater amplifier should include : 

(2) The measurements of all tube and other important operating voltages and 
currents. 

(2) The determination of the frequency response characteristic at various 
volume control settings. 



Aug., 1936] DESIGN AND PRODUCTION OF AMPLIFIERS 187 

(3) The measurement of harmonic distortion in the power output stage at 
various output levels. 

(4) The measurement of the over-all hum level. 

(5) The establishment of whether the amplier is perfectly stable in operation 
at various volume control settings. 

(6) The establishment of whether the microphonic characteristic is sufficiently 
low. 

(7) The establishment of quietness of operation of the volume control through- 
out its range. 

(8) The establishment of proper sound reproduction by actual listening test. 

Theater amplifiers designed and produced in accordance with all 
the above-mentioned considerations should fulfill a very definite 
service in the industry. It is acknowledged that the cost considera- 
tion has not been mentioned. Cost is very important in the design 
and production of equipment of this type, but it should be treated 
as secondary in importance as compared to good and reliable opera- 
tion. 

The author wishes to acknowledge the contributions of J. N. Leh- 
man and J. P. O'Neill in the design work in connection with the 
amplifier illustrated in Fig. 1 and described in the text. 



CONTRIBUTIONS OF TELEPHONE RESEARCH TO SOUND 

PICTURES* 



E. C. WENTE** 

Summary. The principal elements of the sound system for motion pictures are: 
microphone, amplifiers, recorder, reproducer, and loud speaking receivers. The 
evolution of these devices began with the invention of the telephone by Bell. In this 
paper it is shown how subsequent studies relating to the telephone art contributed to 
their development prior to the advent of commercially successful sound pictures. 

The term 'sound picture' signifies a motion picture accompanied by 
sound which is reproduced from a synchronized record. It thus com- 
prises two conjoined but distinct systems. Before the advent of 
sound pictures, silent motion pictures had enjoyed a long successful 
commercial history and had been brought to a high state of technical 
perfection. The sound system came as an adjunct, but has since be- 
come a sine qua non of the commercial motion picture. 

The sound system used in connection with motion pictures is made 
up of a series of devices of which the following are the most essential : 
a microphone, with which sound is translated into corresponding elec- 
tric current; a recording amplifier, with which the weak microphone 
current is transformed into a stronger corresponding current; a re- 
corder, with which the time-pattern of the amplified current is trans- 
lated into a permanently fixed corresponding space-pattern known as 
a sound record; a reproducer, with which the sound record is retrans- 
lated into electric current; a reproducing amplifier, the function of 
which is similar to that of the recording amplifier ; and a loud speaker, 
with which the current from the reproducing amplifier is translated 
into sound. Although it is true that sound has been recorded and re- 
produced for many years without any electrical transformations, as in 
the Edison phonograph, it is unlikely that commercially successful 
sound pictures could ever have been produced by a system which did 
not have incorporated within it each of the above-mentioned devices. 
No sound picture system could succeed until each of them had been 

* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** Bell Telephone Laboratories, Inc., New York, N. Y. 
188 



CONTRIBUTIONS OF TELEPHONE RESEARCH 189 

brought up to a certain standard of perfection, since the performance 
of the system as a whole is largely controlled by the limitations of the 
most imperfect of its several components. From the beginning of 
motion pictures, the addition of sound had been envisaged and vari- 
ous sound systems had been proposed by inventors from time to 
time. These inventors were ahead of their time, not because the 
public was unready to accept sound pictures, but because the various 
necessary elements were undeveloped. It was no more possible to 
build a successful sound system before these devices became available 
than it was possible for Leonardo da Vinci to succeed in his attempt 
to build an airplane before suitable engines were developed and the 
knowledge of aerodynamics had been extended. Fundamentally, the 
history of the sound system for motion pictures resides in the history 
of each of these constituent elements, for the development of which 
no single individual or group of individuals was wholly responsible. 
The impetus for their initial development came for the most part 
from outside the motion picture field. 

The history of the microphone goes back to Alexander Graham 
Bell, who in 1875 first produced a device whereby sound was success- 
fully translated into corresponding electric current. Not only was 
this invention epoch-making in electrical communication, but it also 
was the first step on the way leading to a sound system for motion 
pictures. Bell's extraordinary achievement can be thoroughly ap- 
preciated only by one who knows something of the complexity of 
speech waves and the minuteness of the powers involved. All the two 
billion persons in this world talking at once would not generate enough 
power to propel a modern automobile along a smooth road at a speed 
exceeding the legal limit, yet the microphone of a telephone system 
must operate with but a part of the power of a single voice. More re- 
markable still is the fact that in translating this power we must pre- 
serve the original wave-form. 

The next advance in microphones came with the development of 
the carbon button, to which Berliner, Hughes, Edison, Blake, and 
others contributed. While the carbon button is not used in sound pic- 
ture apparatus, it is of interest to us in that it is the first practical em- 
bodiment of the principle of amplification, for with it the power im- 
parted to a diaphragm by sound waves is translated into a greater 
amount of corresponding electrical power. The carbon microphone 
is eminently suited for commercial telephony. It has exclusively held 
this field throughout the world over a span of several generations. It 



190 E. C. WENTE [j. s. M. p. E. 

is doubtful whether it will ever be displaced in this type of service. 
By a sacrifice in efficiency it can be designed so as to be relatively free 
from distortion. Such instruments have been widely used in radio 
broadcasting and public address systems, but even a high-quality 
carbon microphone is unsuitable for sound picture recording. With 
the distant pick-up conditions that here generally prevail, the sound 
intensity reaching the microphone is considerably less than it is in 
commercial telephony. With the high amplification that is required 
under these circumstances, carbon noise will intrude upon the signal 
to an intolerable extent. 

The microphone which was able to meet the requirements for sound 
picture recording was originally developed, not for any commercial 
purpose, but as a laboratory tool for use in a program of research on 
speech and hearing, initiated by the late Dr. H. D. Arnold and carried 
out under the direct supervision of Dr. H. Fletcher and the late Dr. 
I. B. Crandall. Further objectives in the design of this instrument 
were to provide a means for measuring the performance of telephone 
instruments and to set up a standard microphone for reference pur- 
poses. This microphone was of the condenser type. It was de- 
scribed in the Physical Review in 1917 under the title, "A Condenser 
Transmitter as a Uniformly Sensitive Instrument for the Absolute 
Measurement of Sound Intensity." In this article the possible use of 
the instrument for recording sound upon photographic film was men- 
tioned, although primarily with reference to the study of speech 
sounds. In much the same form as there described it was later used 
in recording sound pictures. The principle of the condenser micro- 
phone was not new. It had been suggested as early as 1881, but was 
wholly impracticable until electric current amplifiers became avail- 
able. It is perhaps in principle the simplest of all types of micro- 
phones, as it comprises merely a pair of plates, one of which is fixed 
and the other movable under the action of sound-waves. It was 
thought originally that its performance could therefore be computed 
from its dimensions, if the movable plate were made in the form of a 
diaphragm. The motion of a free diaphragm under the action of an 
alternating force could be accurately determined by formulas derived 
by previous investigators. However, the actual performance of the 
instrument was found to depart greatly from that which had been 
computed theoretically. It was discovered that the thin layer of air 
between the diaphragm and the fixed plate had a profound influence 
upon the motion of the diaphragm. Means had therefore to be found 



Aug., 1936] CONTRIBUTIONS OF TELEPHONE RESEARCH 191 

for calibrating the instrument. For this purpose a special form of 
thermophone was devised. Although it was disconcerting to find 
that the microphone performed otherwise than was expected, investi- 
gation showed that a proper proportioning of the air-film between the 
two condenser plates afforded an effective means for controlling the 
motion of the diaphragm, and hence the response vs. frequency char- 
acteristic of the instrument. The theory of this control was developed 
by Dr. Crandall. By a change in the dimensions of the film of air 
and by the substitution of a duralumin for a steel diaphragm in 1923, 
a condenser microphone was produced which had a sensitivity 100 
times as great as that of previous models. This microphone was 
sufficiently sensitive to permit the pick-up of ordinary sounds at a 
distance without interference from noise voltages generated in the 
amplifier, whereas the use of the older models under such circum- 
stances would have been impracticable. In various forms the con- 
denser microphone was extensively used in laboratory investigation 
for almost a decade before the advent of sound pictures, and had been 
employed for some time in public address and radio broadcasting 
systems. 

It has already been pointed out that, because of the low translating 
efficiency of a condenser microphone, it became a useful instrument 
only after telephone current amplifiers had been made available. 
Several practical types of amplifiers were developed for long-distance 
telephony, but today amplification of audio-frequency currents is 
almost universally effected by amplifiers of the vacuum tube type. 
The basic element of these amplifiers is the vacuum tube, which was 
developed from the three-electrode audion invented by Dr. L. De 
Forest. Vacuum tubes and amplifier circuits were developed and 
improved in the laboratories of the Western Electric Company so 
that vacuum tube amplifiers suitable for telephone service could be 
manufactured and installed in a transcontinental telephone line in 
1914. In the following year commercial telephone service was in- 
augurated between the east and west coasts of our country. Subse- 
quent improvements, not only in vacuum tubes but in circuits and in 
circuit elements, were made at a number of industrial research labora- 
tories. Amplifiers of low distortion and increased power-carrying 
capacity, which have played an important role in sound pictures, 
were used not only in experimental laboratories but in communication 
and public address systems and in radio broadcasting some time be- 
fore the commercial introduction of sound pictures. 



192 E. C. WENTE [j. s. M. P. E. 

The recorder used for recording sound upon photographic film 
appears to be a device of unique importance to sound pictures. This 
is possibly true as regards the modulated lamps used by Case, De 
Forest, and others, but not of the oscillograph as first used for vari- 
able-width recording nor of the light-valve for variable-density re- 
cording. The oscillograph was invented by Duddell as a means for 
studying the wave-form of alternating currents. The light- valve 
was devised for use in connection with research studies of the physical 
characteristics of speech and music. The chief objectives in the de- 
sign of the light- valve were to obtain a mechanical structure which 
should be stable, respond uniformly throughout the frequency range 
of interest in music, operate with a relatively small amount of power, 
be capable of fully modulating in a linear manner the light reaching a 
film, and transmit enough light to the film to give the photographic 
emulsion a normal exposure. However, these objectives would have 
been without purpose if photographic films of great uniformity, and 
scientific information on processing methods, had not been made 
available by the manufacturers of photographic materials for motion 
pictures. To them the sound engineer is greatly indebted. The light- 
valve was used in the laboratories of the Western Electric Company 
for recording sound upon motion picture film in 1923, and for the com- 
mercial transmission of pictures over telephone lines in 1924, several 
years before sound pictures made by the Western Electric Com- 
pany's equipment were first publicly shown. 

In order to test then* fidelity, the sound records made in the labora- 
tories were reproduced with a photoelectric cell. This was a very 
simple matter, as suitable photoelectric cells had been available for 
some time. One of these cells was merely substituted for the con- 
denser microphone hi the recording amplifier, without any other altera- 
tions in the circuit. 

The last in the sequence of essential elements of the sound system 
is the loud speaker. This also dates from Alexander Graham Bell. 
In his early demonstrations of the telephone receiver he used it as a 
loud speaker, although the loudness was insufficient to permit more 
than three or four persons, while grouped about the receiver, to hear 
the received sound. During the succeeding years numerous patents 
relating to loud speakers were issued. 

Studies at Bell Telephone Laboratories of the characteristics of 
speech and telephone quality were being conducted by means of head 
receivers, which were quite satisfactory for the purpose. However, 



Aug., 1930] CONTRIBUTIONS OF TELEPHONE RESEARCH 193 

the American Telephone and Telegraph Company was called upon 
to deal with the transmission of music as well as speech. The Labora- 
tories therefore undertook the problem of studying music in a way 
similar to that in which speech was being studied. In 1924 a moving- 
coil loud speaker having a direct-radiating diaphragm was used in 
these studies. This loud speaker was designed with no commercial 
application in view but with the idea of obtaining an instrument 
which would operate without introducing an appreciable amount of 
distortion. Unfortunately, it had a rather small output power 
capacity. Studies in hearing, which were carried on at the Labora- 
tories at this time, showed that the quality of music depended upon 
the level at which it was reproduced. For the study of music, there- 
fore, a loud speaker was required that was capable of reproducing 
music at its original loudness level. To satisfy this requirement a 
special loud speaker of the horn type with a moving-coil drive was 
developed. This loud speaker, as regards quality, sound output 
capacity and efficiency, was superior to those previously available. 
It was designed and built purely for laboratory purposes. It was 
some time later that this loud speaker was brought out in commercial 
form by the Western Electric Company and used in the first public 
demonstration of its sound picture system. 

All the essential elements of the sound system as adopted by the 
Western Electric Company were now available, at least in laboratory 
form. All, with the exception of the amplifiers, had come into being 
as instruments for use in laboratory studies of telephone problems. 
They would be here even if we had no sound pictures today. It was 
necessary only that these elements be brought together in proper 
commercial form and the system synchronized for the silent picture 
to become articulate. That event had now become almost 
inevitable. 

It is not our purpose in this paper to discuss the subsequent com- 
mercial history of sound pictures, which in its broad outlines is 
familiar to the reader. Its commercial success was due to numerous 
important contributions, many of them made by forgotten men who, 
working with ingenuity and force, have brought the sound picture to 
its present high state of development. In the laboratory it is possible 
to get along with equipment which functions properly most of the 
time, but in commercial use failure to function is costly in its conse- 
quences. Great credit therefore belongs to the men who trans- 
formed the laboratory apparatus into successful commercial equip- 



194 E. C. WENTE 

ment, and also to the men whose duty it is to see that the equipment 
is kept in operation, often under the most trying circumstances. 

Such rapid technical progress has been made in the few years which 
have elapsed since the introduction of sound pictures that the early 
equipment and methods already seem antiquated. Some of the in- 
struments which have here been described are becoming obsolete. It 
is not likely, however, that a sound system will ever be used in sound 
pictures which does not comprise the sequence of elements here 
enumerated, although the form of the individual devices may undergo 
important changes from time to time. 



NEW HIGH- VACUUM CATHODE RAY TUBES FOR 
RECORDING SOUND* 



M. VON ARDENNE** 



Summary. In Germany the cathode ray tube has assumed a definite though not 
very important role in the field of sound reproduction, and in television it has become 
of such importance that mechanical methods of scanning are rarely considered now- 
adays. 

The paper describes a new high-vacuum cathode ray tube especially designed for 
recording sound, the purpose of the development being to avoid the disadvantages 
inherent in such tubes currently used. The fluorescent line required for recording is 
produced by means of an electrodptical system in which a controlled accelerating 
voltage in the path of the electrons from the cathode constitutes the "lens electrode" 
and achieves the focusing action. The characteristics of the tube are described in 
detail. 

Technical development in various countries can be helped or 
hindered by the influence of the patent situation. The final decision 
as to whether a certain technical advancement is useful or not is in 
no way influenced by the patent situation, and depends only upon 
the intrinsic value of the advancement. 

Under the influence of the situation peculiar to Germany regarding 
patents in the field of sound reproduction, the cathode ray tube has 
assumed a definite though not very important role. On the other 
hand, the cathode ray tube has become of such importance in solving 
problems in the field of television that mechanical methods are 
scarcely considered nowadays. Because of the intensive work that 
has been done with cathode ray tubes in connection with television, 
many fundamental advances have been made, and the technical value 
of using this method for recording sound upon film has been en- 
hanced greatly. 

Until the present time cathode ray tubes, especially those filled with 
gas, have possessed the following disadvantages : 



* Received March, 1935. 
** Berlin, Germany. 

195 



196 



M. VON ARDENNE 



[J. S. M. p. E. 



(1) The properties of the tubes are not constant with time. Usually the 
effective light intensity decreases with the time that the tube is in operation. 

(2) The life of the tube is rather short, due to the bombardment of the cathode 
by positive ions. 




CATHODE 



FIG. 1. The electrooptical path in the new high- 
vacuum tube. 



(5) High-frequency deflections of the light-beam are usually produced par- 
tially in combination with special magnetic fields. 

(4) The fluorescent spot or line is not free from parasitic disturbance by the 
control device. 

(5) For distortionless reproduction the tubes can not be heated with alternat- 
ing current. 

(6) As is the case with other kinds of recording apparatus, the light intensity 
is often too low. 

With the new form of tube construction to be described, the 




FIG. 2. Line-sound-film tube with combined variable- 
intensity and variable-amplitude characteristic. 



above-mentioned disadvantages are eliminated. The new tubes have 
been developed for recording sound with the benefit of experience 
gained in designing and constructing television tubes. 

With respect to establishing the path of the rays and the applica- 
tions of "electrostatic" optics, the aspects are the same as described 
in the above-mentioned work. The main difference between the tube 
that is used in television and the one that is used for recording sound is 



Aug., 1936] 



NEW CATHODE RAY TUBES 



197 



that in the latter case it is desired to have a fluorescent line whose 
intensity can be controlled, rather than a spot. This result can be 
attained by means of "electrooptical" cylindrical lenses, and with 
such an arrangement the same configuration for the concentrating 
and accelerating fields will exist for all electrons that are emitted 
from the cathode. Small differences in 
this configuration are enough to 
cause large differences in the dis- 
tribution of light on the fluorescent 
line. 

Another difference in comparison 
with the tubes used in television 
is that no scanning is necessary, 
and therefore the fluorescent screen 
can be very close to the ray-pro- 
ducing system. The maximum at- 
tainable light intensity at a spot is 
much greater as a result of this 
smaller distance, and is dependent 
upon the saturation and fatigue 
characteristics of the fluorescent 
screen. 

A complete discussion of the 
"electrooptical" system, the in- 
fluence of the space-charge upon 
the line width, and the determina- 
tion of the proper point upon the 
cathode emission characteristic curve 
at which to work, will not be 
given here. It will be sufficient to 
describe the most important proper- 
ties of the completed tube ; and only 
so far as they apply to recording 
sound upon film. 

The "electrooptical" path is shown in Fig. 1. The electrons, 
emitted from the indirectly heated oxide-coated cathode, are pro- 
pelled under the influence of the accelerating field produced by 
the positive voltage UL of several hundred volts. This accelerating 
field will be more or less offset by the negative bias voltage U g of the 
light-control electrode. This electrode works exactly in the manner 




FIG. 3. Line-sound-film tube 
(normal product) with two cylin- 
drical lenses in the electroopti- 
cal system. 



198 



M. VON ARDENNE 



[J. S. M. p. E. 



of the negatively biased control-grid of a modern amplifier tube. 
The control-grid does not take any appreciable energy. The "focus- 
ing action" of the first accelerating field always remains so strong 
that the divergence of the electron beam after passing the first ac- 




FIG. 4. Unretouched photograph of the 
fluorescent screen, showing the sharpness 
of the line and uniform intensity of illumi- 
nation of the tube of Fig. 3. 



celerating field will not be so large that the electrons will pass directly 
to the electrodes of the second accelerating field. The second ac- 
celerating field is built up between the main anode and the so-called 
"lens-electrode" by the difference between the anode voltage U a and 
the lens voltage UL- It works principally as a concentrating lens. 
For a given anode voltage there will be a value of lens voltage that 
will produce a sharp spot (or line) upon the fluorescent screen. 




FIG. 5. Photograph of the complete tube. 



A tube similar to the one represented diagrammatically in Fig. 1, is 
shown in Fig. 2. With this tube, in addition to the light intensity 
modulation, there is a corresponding change in length of the fluores- 
cent line. The length of the fluorescent line, or the recording ampli- 
tude, becomes small when the control voltage is adjusted to produce 
a less intense line of light, and thus the changes in amplitude and 
intensity aid one another. 



Aug., 1936] 



NEW CATHODE RAY TUBES 



199 



leu 



For a pure "intensity-control" the author has developed the system 
shown in Fig. 3. In this form the tube has scarcely any resemblance 
to the common cathode ray tube, but is much more like the typical 
amplifier tubes employing 
cylindrical electrodes. In 
this case, however, due to 
the higher voltages em- 
ployed, greater distances be- 
tween the electrodes are 
necessary. Because of the 
cylindrical arrangement of 
the electrodes, all electrons 
coming from the cathode are 
concentrated and accelerated 
to the same extent. The 
methods of supporting the 
electrodes insure a good 
symmetrical system and one 
that will remain in condi- 
tion after use. The constant 
intensity of illumination and 
width of the fluorescent line 



U a 3,000 VOLT 
U u TO^ OF Uo. 

LtNQTH OF LINE.- AO. mm. 
WIDTH OF LINE, a 0.5 mm. 



U 9 -30 -TLO 



-10 



FIG. 6. 



Characteristic curve of the tube 

of Fig. 3. 
are shown in the unre- 

touched photograph of Fig. 4. Under the influence of the con- 
trol voltage, the intensity of illumination varies equally along the 

entire line, while the 

100% r~ r\ width remains prac- 

tically unaltered. The 
fluorescent line has a 
width of less than 0.5 
mm. and a length of 4 
cm., and can be made to 
assume other dimensions 
if desired. The position 
of the line is entirely 
free from disturbance 
by the control device. 



50 




TOO 



600 



500 



-4-00 



FIG. 7. 



Spectral distribution of intensity of the 
fluorescent screen (absolute). 



As a result of experience gained in constructing television tubes 
it is possible to design for greater or lesser amplitudes. In addition, 
the position of the fluorescent line is not influenced by using alternat- 



200 M. VON ARDENNE 

ing current on the indirectly heated cathode. The various slits that 
cause the lens effect are plainly shown in Fig. 3. The dimensions of 
the tube differ greatly from those of the older types of tubes, as shown 
in Fig. 5. When the working voltage is once attained there is no 
need of making additional changes. In this respect the analogy be- 
tween this tube and the common amplifier is quite clear. As a 
high-vacuum tube the life is scarcely any shorter than that of an 
incandescent lamp or amplifier tube. With the old tubes a voltage 
swing of 20 to 50 volts was necessary; whereas, with this new type, 
10 volts is enough to produce light to dark modulation. The char- 
acteristic curve of the tube shown in Fig. 3 is given in Fig. 6. The 
spectral distribution of intensity for the normal calcium tungstate 




FIG. 8. Spectrum of the calcium tungstate 
screen. 

screen is shown in Fig. 7, and a photograph taken on a super-pan 
plate of this spectrum is given in Fig. 8. 

The light intensity is sufficient to allow photographs to be made 
directly upon positive film. In addition, it is possible to achieve 
still greater light intensities with an increase in anode potential with- 
out the disadvantages heretofore encountered. Larger anode currents 
can be obtained by changing the dimensions of the system. It should 
be noted that for the same anode current, a high- vacuum tube will 
produce a much greater light intensity than one of the older gas- 
filled tubes. In the latter case, a large percentage of the electrons 
does not reach the screen due to the scattering effect. 

The plate input, in the tube here described, is less than one watt, 
under normal operation, which is less than the input to other devices 
used in recording sound, such as Kerr cells, glow lamps, etc. With 
such a small input it is possible to produce this voltage by means of 
small apparatus, having protective resistances for reducing the 
danger of the high voltage. The control power is also considerably 
less than that commonly necessary. The system is entirely inde- 
pendent of frequency in the region of medium and high frequencies. 



AN EXPERIMENTAL PROGRAM IN VISUAL EDUCATION* 

F. H. CON ANT** 



Summary. A discussion of experimental work now being carried on at the Massa- 
chusetts Institute of Technology on a program of visual education designed to facilitate 
teaching in the fields of science and engineering. The use of animation and the 
technic of its application in the first of a series of films showing the behavior of an 
electrical wave travelling along a 250-mile power transmission line, are described. 
Other films are considered and the possibilities of animation in other fields of technical 
training are indicated. 

Early last year the Massachusetts Institute of Technology be- 
gan an experimental program to investigate the value of motion 
pictures as an aid in teaching some of the more difficult subjects in 
science and engineering. The first step in this undertaking was to 
obtain from members of the instructing staff (1) a broad concept 
of the field to be covered, (2} suggestions for specific subjects, and (3) 
methods of presentation designed to give the maximum assistance 
in teaching students in various stages of technical training. 

A representative group of members of the faculty was asked to 
determine whether the proposed films should be silent or sound pro- 
ductions. The decision favored silent films with adequate explanatory 
titles, on the ground that teachers would have greater latitude in 
interpreting the subject. It was decided, however, that all films 
should be made with sound aperture, thus permitting the addition 
of a sound-track if such seemed desirable in the future. The pro- 
duction of silent films aided in keeping costs within the limits of a 
modest budget and assured a certain flexibility by permitting changes 
or additions from time to time. Among the many subjects suggested 
were such interesting possibilities as the operation of complex ma- 
chinery, principles of physics, problems of human relations, time 
studies, and mathematical problems. 

One of the most interesting objectives of the program was to 
investigate the possibilities of animation as a means of teaching 

* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** Massachusetts Institute of Technology, Cambridge, Mass. 

201 



202 F. H. CONANT [j. s. M. p. E. 

subjects that often are difficult for students to visualize. Such sub- 
jects, or individual problems in some instances, lie not only in the 
field of undergraduate education, but in the advanced work of 
graduate students. 

Having laid the groundwork for the program, the task of film pro- 
duction was made the responsibility of the Institute's Photographic 
Service under the direction of the author. In planning technical 
procedure and in adapting the subjects to scenario form he has had 
the very valuable cooperation of Professor A. C. Hardy of the De- 
partment of Physics, and Mr. F. Ramsdell of the Worcester Film 
Corporation. 

The first production was an animated film in the field of electrical 
phenomena. The subject, Traveling Waves on Transmission Lines, 
was chosen because travelling waves undergo a variation with distance as 
well as with time, a characteristic that made them difficult to visualize 
and therefore encouraged the attempt to produce the phenomena in 
animated form. The film is a combination of scenes photographed 
in the field and animation showing the behavior of a wave on a 
250-mile transmission line with open end. The production was 
based upon a laboratory study made by Professor L. F. Woodruff of 
the Department of Electrical Engineering, and was designed to be 
one of a series of thirteen films presenting complex electrical pheno- 
mena in animated form. The success of the first film led to the pro- 
duction of the second and third of the series, dealing with voltage 
waves on a short-circuited line. 

The technic of animation developed by Professor Woodruff may 
be of some interest, for it entailed the problem of translating complex 
phenomena to a visual form readily understood by advanced students 
in electrical engineering. Since mathematical analysis has not yet 
reached the degree of development whereby travelling wave distribu- 
tions may be calculated accurately, they were determined experimen- 
tally on an artificial line in the Institute's dynamo laboratory. A 
cathode-ray oscillograph control circuit was designed by Professor 
Woodruff, by means of which a succession of identical transients was 
produced, and curves of the sending-end voltage and the voltage at 
another point of the line were thrown upon the screen of the oscillo- 
graph. Oscillograms were made at each section (32 sections form a 
250-mile line), and from enlargements of these oscillograms was plotted 
the wave distribution at intervals of an eighth of the line. An assis- 
tant then made celluloid templates to match the curves thus laid out. 



Aug., 1936] VISUAL EDUCATION 203 

The next step was to cut silhouette forms of the waves from medium- 
tone paper, and to interpolate between these laid-out curves to pro- 
duce additional intermediate curves. In some parts of the travel, 
where sudden changes of shape took place, it was necessary to lay out 
each curve individually. 

The electrical wave films were photographed upon a standard 
animation stand, lent to the Institute's photographic service by the 
Eastman Kodak Company. A drawing-board was fitted with regis- 
tration pins identical to those on the platen of the animation stand, 
and sheets of white paper 9 X 12 inches in size were punched to fit 
the pins. A celluloid template with a rectangular cut-out and regis- 
tration holes was placed over each sheet, and lines were drawn to 
indicate the bottom and left edge of the silhouette wave-forms. 
These forms were then pasted upon the paper sheets. The back- 
ground of line, voltage scale, and generator were drawn upon another 
master template. Each wave-form was photographed through this 
template, which produced a uniform background in which the only 
animation was the closing of a switch, titles, and the change in wave- 
form as the wave moved along the transmission line. For the first 
three trips along the line it was found necessary to use 128 diagrams 
per transversal. Since the action dies down considerably from that 
point on, 64 diagrams, using two frames per diagram, were satisfactory 
for the remainder of the film. When projected in our lecture halls 
the scale is approximately half an inch to the mile, and the time re- 
duction for producing the travelling wave in animation is of the order 
of 7500 to 1. A total of nearly 1500 silhouette wave-forms was 
used for each film. 

In addition to the electrical films, the Institute has produced an- 
other, entitled The Graphic Representation of Machine Operations. 
This film, which opens with detailed views of a machine drawing, 
and then shows the various machining operations necessary to pro- 
duce the parts shown in the drawing, is of an elementary nature. It 
was designed as an introduction to an animated film on descriptive 
geometry, which we hope to produce for the purpose of assisting 
first-year students to visualize three-dimensional concepts. 

Although these films were produced for instructional purposes at 
the Institute, they are also available for loan to other educational 
institutions and to professional groups who may be interested in 
seeing them. 



IS THE FEDERAL GOVERNMENT INTERESTED IN 
EDUCATIONAL FILMS?* 



C. M. KOON** 

Summary. A review of the film activities of various Federal agencies is presented, 
their educational significance suggested, and some general observations are made as to 
the Federal Government's interest in educational films. In conclusion, the vast 
potentialities of the educational film field are discussed and the part the Federal Gov- 
ernment might play in its development pointed out. 

If one were to judge the Government's interest in educational films 
by Federal laws on the subject, he would be forced to consider that 
there was no interest. A more careful consideration of Government 
activities, however, reveals that the United States signed the 
Geneva Convention to Facilitate the International Exchange of Educa- 
tional Films by agreeing to admit such films free of duty. It also sent 
an official delegation to the International Congress on Educational 
Cinematography which was held at Rome in April, 1934. When 
approached personally, some high Government officials have indicated 
a very definite interest in the use of motion pictures for instructional 
purposes, but this interest has not found expression in a centralized 
motion picture service. 

Therefore, one must turn to the various bureaus and Federal 
agencies and study their motion picture activities as a means of 
determining their interest in educational films. At least fifteen 
agencies in the Federal Government make, distribute, use, or publi- 
cize motion pictures as part of their regular functions. The film work 
lies mainly in the field of service to the farmer, the teacher, the CCC 
camp educational adviser, and the motion picture producer who 
wants to sell his films abroad. 

By far the most extensive motion picture services of any of the 
Federal departments are carried on by the War and Navy 
Departments, principally for entertainment and training purposes, 
and by the Interior and Agriculture Departments, principally for 

* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** U. S. Department of the Interior, Office of Education, Washington, D. C. 
204 



EDUCATIONAL FILMS 205 

instructional purposes. As a rule, Government films are available 
to responsible groups without cost, excepting transportation charges. 
The motion picture production and distribution activities of the 
various Federal agencies will be considered individually. 

A small but well equipped motion picture studio, laboratory, and 
office are maintained by the Department of Agriculture. The service 
is unique inasmuch as it was the first organized effort upon the part 
of the Government to use motion pictures for instructional purposes. 
It is unique also because it is the only institution of its kind exclusively 
devoted to the production and distribution of instructional pictures 
on agriculture, forestry, conservation, rural engineering, and home 
economics. 

Films produced illustrate how to raise and care for cattle, horses, 
swine, sheep, and poultry; how to produce crops of all kinds, com- 
bat injurious insects and diseases of livestock and plants; cope with 
engineering problems on the farm; build roads and trails; and how 
to care for the home and the family. They inform as to Federal 
regulations concerning animals, forests, crops, insects, rural engineer- 
ing, and marketing. They convey to the public in general, and to 
rural dwellers in particular, the information and discoveries emanating 
from the scientific investigations of the Department of Agriculture. 

The Department's film library numbers about 300 subjects, of which 
some 4000 copies are being distributed by the Department. At 
least an equal number of copies have been purchased by organizations 
and state, federal, and foreign governmental agencies interested in 
disseminating the information contained in the films. No record is 
available of the extent of the distribution of these purchased copies. 
However, since they are selected subjects, the circulation probably 
is greater than that of the films distributed by the Department. 
During the fiscal year 1934-35, actual reported attendance totalled 
about 2,115,000 for about 75 per cent of the borrowers. 

Designed to aid in the work of extension and field workers, the 
primary use of the Department's films is by or under the supervision 
of such workers. However, loans are made to farmers' organiza- 
tions, schools, colleges, churches, theaters, and other agencies or 
persons whenever copies of the desired pictures are available. The 
supply of copies, however, is not nearly large enough to meet such 
demands, and hundreds of requests have to be turned down annually. 

The film activities of the Department of the Interior are not cen- 
tralized as they are in the Department of Agriculture, but are carried 



206 C. M. KOON [j. s. M. p. E. 

on by various bureaus within the Department.* The Bureau of 
Mines and the National Park Service are the most active. 

The United States Bureau of Mines of the Department of the 
Interior has in its library of motion picture films approximately 
3000 reels of silent pictures. These pictures are produced in coopera- 
tion with members of the minerals and allied industries for the 
purpose of disseminating information about mining methods and 
practices. Numerous subjects pertaining to principles of safety and 
first-aid are used for training purposes. 

During the fiscal year the Bureau's films were shown on 61,010 
occasions to an attendance of approximately 5,000,000 persons. The 
figures given above represent an increase of 23 per cent over the pre- 
ceding year, and it is estimated that an even larger increase will 
take place during the coming year. About four-fifths of the requests 
at the present time are for the 16-mm. size. 

The Bureau does not engage a production staff, nor does it do any 
laboratory work whatever. All expenses incidental to the production 
of these films and prints are paid by industries and their associations. 

Letters and words of commendation regarding the inestimable 
value of these films for purely educational purposes have been re- 
ceived from, universities, high schools, and elementary schools 
throughout the country. The demand for the Bureau's films at this 
time far exceeds the available supply. 

For many years the National Park Service has taken films of the 
parks, to record their natural beauties and encourage travel. Last 
year this service underwent considerable expansion by undertaking 
to circulate educational films in the CCC camps located in state or 
national parks. About 300 subjects were obtained from various 
sources mostly outside the Government, and an excellent service 
was rendered to the camps, causing an increased demand for the 
establishment of a centralized film service for all the camps. In addi- 
tion to this distribution service, National Park Service cameramen have 
filmed the activities of the various camps themselves, showing the 
types of work that have been undertaken and the methods of train- 
ing the enrolled personnel. About 30 reels have been completed and 
are available on usual Government terms. The Park Service also has 
cooperated with the University of Chicago and with Erpi Picture 

* A central Motion Picture Division has been established in the Department 
of the Interior since this article was written. 



Aug., 1936] EDUCATIONAL FILMS 207 

Consultants, Inc., in making six sound subjects on physical geology 
which are intended for instructional purposes and which may be 
obtained from a number of agencies. 

The Bureau of Reclamation has a number of silent films in circula- 
tion. These films show the engineering, agricultural, and economic 
development of the various Federal reclamation projects, and are 
used extensively in schools and colleges. 

The United States Public Health Service of the Treasury Depart- 
ment has made a few films dealing with special phases of public 
health work which are used for exhibition before medical societies 
and other special audiences. The Women's Bureau of the United 
States Department of Labor has produced and is circulating four 
films dealing with employment conditions of wage-earning women. 
The Tennessee Valley Authority has produced four films during the 
past year which are available for general distribution. These films 
depict the work being done in the Tennessee Valley. The Federal 
Housing Administration has had a number of films produced for 
theatrical showings, which are now being released for school and 
club use. Two films depicting the activities of relief workers were 
produced in Los Angeles last spring under the auspices of the Federal 
Emergency Relief Administration; and this fall a Motion Picture 
Record Division has been established by the Works Progress Adminis- 
tration to record the progress on public works projects. 

The combined yearly attendance at all the exhibitions of the 
Government's educational films amounts to only about 10,000,000 
persons or one day's attendance at motion picture theaters. If all 
those who attended these Government showings were school pupils 
it would take more than three years for the 31,000,000 school children 
of America to attend one showing. 

In addition to the agencies that actually produce and distribute 
motion pictures, a few Federal agencies carry on other motion picture 
activities. The Motion Picture Section of the Bureau of Foreign 
and Domestic Commerce exists for the purpose of promoting and 
developing the motion picture business in the United States and 
abroad. It keeps in close contact with the foreign departments of 
the individual producing and distributing companies ; with the vari- 
ous trade associations in the industry; and with every possible source 
of reliable information both at home and overseas. It publishes this 
information in bulletins and pamphlets, as a means of extending every 
possible assistance in organizing, developing, and maintaining a 



208 C. M. KOON [j. s. M. p. E. 

profitable export business for American producers and distributors of 
entertainment films; manufacturers and sellers of motion picture 
equipment; and producers, distributors, and exhibitors of non- 
theatrical (industrial and educational) films. Nothing is left undone 
to keep open the legitimate arteries of business and therein lies the 
answer to what has been characterized so generously by the motion 
picture industry as "a job well done." 

A service of altogether different type is being launched by the 
Motion Picture and Sound Recording Division of the National 
Archives. This division is concerned with the acquisition, storage, 
maintenance, and cataloguing of historical activities of the United 
States. It has also the responsibility of arranging for recording im- 
portant historical events upon film or disk; and the reproduction and 
distribution of films and recordings of historical value for the conveni- 
ence of Government departments and educational agencies. It is 
interesting to note that the National Archives is the first central 
depository of all Government films, and is arranging projection rooms 
for their exhibition along with other meritorious films. 

In harmony with the general function of the United States Office 
of Education, the Radio and Visual Education Section serves as a 
national clearing house for the exchange of information about the 
production, distribution, and use of motion pictures for educational 
purposes. 

Scarcely a week passes but an urgent request is made upon the 
United States Office of Education to take a more active part in having 
films made and distributed to the CCC camps and schools of the 
Nation. Other plans call for some form of Federal aid to schools for 
purchasing equipment to assist in the school motion picture work. 
Judging from the large number of plans and requests for grants from 
the four billion dollar relief fund, many persons in or near the motion 
picture industry believe that the Government should assist further 
in the development of the educational film field. 

The Office of Education is also interested in extending and facili- 
tating the use of films for educational purposes. That is the reason 
for the title selected for this paper: "Is the Federal Government 
Interested in Educational Films?" The answer is that various 
bureaus and independent agencies within the Federal Government 
are interested, but there is a woeful lack of coordination of the work 
of these agencies. In fact, from the standpoint of educational service, 
the whole non-theatrical field is chaotic and disorganized. 



Aug., 1936] EDUCATIONAL FILMS 209 

Extensive research and experimentation have demonstrated that 
the motion picture has great educational value. Many books, 
monographs, and articles have been written and addresses delivered 
before such bodies as the Society of Motion Picture Engineers to 
stress the innumerable Ways in which the motion picture can be used 
to aid education. Yet, less than ten per cent of the 276,000 schools 
in the United States make systematic use of motion pictures for 
instructional purposes, and they do not make ten per cent of the use 
of the film they would make if an adequate supply of suitable films 
were available. More than $3,000,000,000 is spent annually on educa- 
tion in the United States, and over a million teachers employed. In 
addition to the potential school market with its millions to be served, 
the CCC camps, and tens of thousands of clubs need specialized 
educational film service. A survey of the educational film field made 
by the Office of Education 1 about a year and a half ago indicated 
beyond a doubt that an American film institute should be established 
to facilitate the production, distribution, and use of educational films. 

At first it was deemed wise for the Office of Education to take the 
initiative in the formation of the institute, with the Government, 
organized education, and the motion picture industry all participating. 
Later, however, the American Council on Education, a non-govern- 
mental agency, took the initiative, and is now sponsoring the estab- 
lishment of such an institute. 

It is not contemplated that a new producing industry would be 
set up in Washington or elsewhere. Instead, it is definitely recognized 
that the motion picture industry should be expected to come forward 
and use its expert technical services for supplying the numerous films, 
projectors, and other equipment necessary to make an efficient 
accomplishment of this vastly needed service. Members of the SMPE 
can render invaluable assistance by developing tougher, more durable 
film; more uniformly good reductions of 35-mm. to 16-mm; and a 
16-mm. combination sound-silent projector that requires little skill to 
operate and a minimum of servicing not to overlook the need for 
international standardization of sprocket placement, and so forth. 
Close collaboration of educators, motion picture producers, and 
government officials is needed if the vast potentialities of the educa- 
tional film are to be developed. 

REFERENCE 

1 KOON, C. M., and others: "Motion Pictures in Education in the United 
States," Univ. of Chicago Press, Chicago, 111. (1934). 



A NON-THEATRICAL, INTERNATIONAL SERVICE 

ORGANIZATION THE AMATEUR 

CINEMA LEAGUE* 



R. W. WINTON** 

Summary. After discussing briefly the evolution of non-theatrical motion 
pictures, particularly of the amateur type, and discussing briefly the technical and 
practical requisites of the non-theatrical filmer, the organization of the Amateur 
Cinema League is described and its aims and purposes discussed. 

Discussion of a non-theatrical, international service organization 
in the motion picture field before this body is logical because the 
Society of Motion Picture Engineers has always interested itself in 
the non- theatrical, as well as the theatrical application of the medium. 

Early years of motion pictures were chiefly theatrical years, be- 
cause the abstract thinker, the scientist, and the technician followed, 
rather than preceded, the exploiter and practical user. Based, to be 
sure, upon very original and quite scientific experiments, the actual 
birth of the movie took place in the showman's booth and not in the 
laboratory. 

During this phase of evolution, non-theatrical pictures were often 
studio by-products, made either by studios themselves, by technicians 
of studios in periods between studio assignments, or by free-lance 
newsreel cameramen whose chief revenue came from studio sales. 
The studio technic and the studio mystery surrounded non-theatrical 
as well as theatrical films, and the non-theatrical user took what the 
studio system gave him. He was continually dissatisfied with what 
he got particularly the educator and the non-commercial projec- 
tionist and the industrial advertiser soon found that his early hope 
of persuading paying theater patrons to look at his sales pictures was 
vain. Storage vaults of business concerns still carry some of these 
failures. The theatrical film industry was too much occupied with 
photoplays to divert its attention to exploiting the non-theatrical 
field. 

* Presented at the Fall, 1935, Meeting at Washington, D. C. 
** Amateur Cinema League, Inc., New York, N. Y. 

210 



THE AMATEUR CINEMA LEAGUE 211 

Somewhat over a decade ago, the practical application of sub- 
standard film set in motion a series of events that changed the status 
of non-theatrical movies from that of a subservient and incidental 
concomitant of theatrical pictures to that of an increasingly indepen- 
dent activity. Before the amateur movie had time to congeal into 
any set category, as had the theatrical photoplay, personal filmers 
were widening the definition of movie amateur into a broader mean- 
ing, and were producing with a hastily improvised technic, what has 
actually become a well recognized, non-theatrical type of movie. 
This new type includes films made for family records; travel movies; 
experiments in scenic pictures made with artistic intent; tentative, 
and sometimes full fledged, photoplays; studies of athletic form and 
records of games all these of the extremely personal character in 
the non-theatrical film category. The new type includes also medical 
and surgical films, pictures made by the scientist either to illustrate a 
difficult process or to be used in instruction; movies produced by 
manufacturers and retailers, either to sell products to the public or 
to train employees; and films designed to accomplish propaganda 
of various kinds. These listings are by no means exhaustive. In 
general, it may be said that films are now used for almost as many 
purposes as is the printed word. 

This extensive development of non-theatrical films, both for 
personal recreation and for practical application, has taken place on 
all the various film widths that have been made available. In general, 
cost has limited the majority of these non-theatrical movie ventures 
to sub-standard widths, although 35-mm. is used also. The impor- 
tant fact in this development is found in the liberation of non- 
theatrical filming from studio methods. As a matter of fact, non- 
theatrical filming has, from the very first, been so different from 
photoplay making that the usual studio technic has not been properly 
applicable. Paradoxically, the typically equipped studio is unsuited 
to non-theatrical filming, and the studio personnel finds it difficult 
to refrain from employing elaborate equipment to handle simple 
situations, which propensity is likely to impart to a non-theatrical 
film a theatrical elaborateness that often defeats the real purpose of 
the effort. 

There are certain considerations inevitable in discovering the 
underlying bases of non-theatrical filming, a lack of which may make 
for failure in such enterprises. One of these is the cost of film and 
equipment. In theatrical production, the expense involved may 



212 R. W. WlNTON [J. S. M. P. E. 

generally be treated as a kind of rough revolving fund, because the 
picture is to be distributed upon the basis of direct sale, lease, or 
rental; and money will be received as a specific and definite result 
of the transaction. This revolving fund theory is not valid with 
non-theatrical pictures, except in a very small minority of instances, 
and whatever cost is incurred is absolute, with the returns either in 
terms of personal satisfaction, reaction, service, or in terms of in- 
direct financial profit that can not be predicted with any certainty. 

Since the greatest amount of non-theatrical filming is done by 
individuals, either as amateurs or practical movie makers, another 
consideration is that of simplicity of equipment. The elements here 
are facility of handling with complexities and technical difficulties 
brought to the lowest degree and easy portability. As an example 
of this requisite of simplicity, the use of a tripod, which is a sine qua 
non of theatrical camera work, becomes an ever-present problem with 
the personal filmer. He must balance the unquestioned advantage 
of this important filming aid against the difficulty of employing it, 
both because of the commotion he will create by setting it up in a 
crowded place, and because of the addition of its weight and bulk to 
that of the other equipment he must take with him, such as exposure 
and distance meters, filters, extra film, and other accessories. 

Study and training are requisites for the non-theatrical filmer who 
is not a product of the apprentice and experience school, as is gen- 
erally the case with the studio worker. The character and scope of 
this training is a third basic consideration in any attempt to serve 
non-theatrical workers. An obvious division of instruction is found 
in the study of how to use the mechanical tools, camera, film, and ac- 
cessories, and what to do with the tools, once one has learned their 
use which gives us two pedagogical subjects, camera technic and 
continuity. This all-around training is not followed in the education 
of theatrical filmers, where the studio organization is so complex that 
specialists are developed to meet each need as it arises. In non- 
theatrical filming, the technic of direction, which bulks so large in 
studio work, assumes a very modest proportion, and the non-thea- 
trical worker who deals more largely with inanimate than with ani- 
mate subjects, or who, in dealing with animate subjects is more 
concerned with catching their natural actions than with inspiring 
them to dramatic efforts, must chiefly learn the art of making the 
people whom he films unself conscious, so that his records may be 
authentic rather than theatrical. 



Aug., 1936] THE AMATEUR CINEMA LEAGUE 213 

After the non-theatrical picture is shot, there arises the problem 
of processing it and the concomitant question of reproducing it in 
distributable quantity, if such is necessary to the purpose. Suitable 
projection for all the different conditions in which non-theatrical 
films are shown is a problem so familiar that it need not be elaborated. 
It is felt desirable only to emphasize again that blindly following 
theatrical standards in projection will never solve the difficulties of 
non-theatrical showings. 

The final considerations in determining what shall be an adequate 
service to non-theatrical film workers are those of distribution and 
the care of film prints. The latter is relatively easy, allowing for the 
ever-present factor of human carelessness; but the former has been 
the rock upon which not a few commercial non-theatrical filmers 
have come to disaster. Distribution is a chore and an unpleasant one. 
The purely personal and non-commercial filmers are popularly sup- 
posed not to be concerned with it, but the experience of a decade in 
working with them has shown that these movie makers hunger for 
audiences just as strongly as do the owners of a typical "industrial" 
who have invested a sizable amount of money in a filming venture. 

Upon the underlying bases of non-theatrical filming just discussed, 
it is possible to construct an analysis of the duties of a service organi- 
zation for non-theatrical movie makers. Since filming is a world- wide 
activity, a non-theatrical movie service body should find aids that 
can be offered to those both far from and close to its headquarters 
and should not neglect its distant members. Since the facilities of 
such an organization are to be offered to all its members, it must meet 
the largest demand most fully, and must take care that its special 
services do not overshadow the general and absorb too much of the 
time and effort of the staff. It must not forget the important duty 
of propaganda and the popularization of non-theatrical filming in 
all its phases. It must serve a continuous crop of beginning filmers, 
and it must guard against the danger of a formalized routine whose 
lifelessness can not be concealed from the students. 

Such a service body must not be entrapped by technicalities or 
technical nomenclature. Non-theatrical filmers lack terminologies 
and nomenclatures and are generally disinclined to acquire them. 
If the counsel they receive is couched in the shorthand of technical 
terms, they will often reject it and become irritable toward those who 
offer it. Opposed to this danger of becoming too technically complex 
in statement is the other peril of appearing too puerile. Probably 



214 R. W. WlNTON [J. S. M. P. E 

a safe course is first to make certain, by examination and reexamina- 
tion, of the accuracy of the facts and the soundness of the advice 
presented, and then to state these in language of great simplicity, free 
from special terminology, so far as may be. 

Our service body must establish early and mutually respectful 
relations with the industry that supplies the tools of non-theatrical 
filming. The easy path would be for it to draw aside its skirts from 
any contact with commercial enterprises and to announce that it 
stands boldly for the interests of the user, as opposed to those of the 
seller. However, unless a service body commands the respect of the 
industry that supplies non-theatrical filming tools, it can not make 
any effective recommendations to that industry on the important 
matters of the nature and cost of the equipment offered, which is 
certainly one of its major obligations. It must recognize manufactur- 
ing and distribution problems and avoid taking any illogical view- 
point allegedly in the interests of users as opposed to those of pur- 
veyors. It must and can serve to translate the attitude of movie 
makers for the supplying industry and that of the industry for filmers. 
This service body must be willing to undertake activity that lies in 
the no-man's land between purveyor and consumer of cinematographic 
goods, and it must, at times, risk being misunderstood by both. As a 
specific example of this work, there may be mentioned the question of 
the distribution of non-theatrical films to their audiences, for which no 
very satisfactory answer has yet been found. In venturing into 
these twilight zone activities, our service organization must not 
permit itself to be led into commercial enterprises. 

Founded upon the basic considerations and conscious of the duties 
that have been outlined, an international non-theatrical movie 
service body might develop its program in the following terms : 

(1) A training system divided into the two broad departments of equipment 
technic and continuity, serving beginners and advanced workers equally well and 
meeting individual needs of members as they arise. 

(2) An information and stimulation system, to publish periodical and oc- 
casional magazines, books, and shorter items. 

(5) A film examination and criticism system. 

(4) A system of aid to other organizations of a non-commercial kind. 

(5) A system of cooperation with commercial concerns, for the broad develop- 
ment of non-theatrical filming. 

(6) A system of service for special fields and special problems. 

(7) A method of dealing with international, national, and regional problems, 
based upon the concept of service without domination or regimentation. 



Aug., 1936] THE AMATEUR CINEMA LEAGUE 215 

We have considered what might be termed the ideal yardstick by 
which the organization and operation of our service body could be 
measured. In order that we may compare the actual to the ideal, it 
will now be desirable to sketch briefly what the Amateur Cinema 
League has accomplished in working out a part of this program. 

Founded in 1926, the Amateur Cinema League now serves non- 
theatrical filmers in more than sixty countries of the world. It is 
owned and controlled entirely by its membership and enjoys no 
grants or subsidies from any source. It makes no profits for any 
stockholders, as it is without capital stock, and it is entirely free from 
any outside control or influence. 

The first need of the League, in its organization year, was to de- 
velop a unity and a solidarity among film amateurs. This was ac- 
complished by the publication of its monthly magazine, Movie 
Makers; by aid to local groups in setting up filming, discussion, and 
photoplay-making clubs; and by the establishment of a system of 
exchanging films from one member to another. By these means, 
isolated movie makers became aware of each other and found 
a method of exchanging experiences and comparing technics. All 
three activities have been maintained and expanded. 

The League had to provide service, but first it had to create this 
service. It may be said that the present technic of non-theatrical 
film training and service that the League employs has been developed 
largely from the observation of the work of League members, as they 
first tried to parallel Hollywood and then diverged from Hollywood 
standards and methods. The first calls for help from amateurs were 
in the field of photoplays, and scenarios of any and every kind were 
eagerly sought by them. Later, the more basic and lasting matters 
of how to make family, travel, business, and scientific films intelligible 
in terms of cinematic grammar began to interest non-theatrical 
filmers, and that distinctly new thing, the continuity of simple, 
non-theatrical movies, emerged into reality. In all this service, we 
had continually to emphasize simplicity and non-technical clarity. 
In addition to this consulting aid to members, the League under- 
took the publication of special bulletins and monographs, because 
the space in its monthly magazine was found insufficient to cover 
certain topics exhaustively. Later, there developed what is now 
accepted as the basic text of non-theatrical filming, Making Better 
Movies, now in its second edition. Film examination and criti- 
cism began early and have increased extensively, and the League has 



216 R. W. WINTON [J. S. M. P. E. 

aided in planning and advising on the filming of pictures of every 
conceivable type for members in every corner of the earth, discussing 
with the authors of the enterprises the kind of equipment to use, 
the treatment, the working out of the treatment, the titling, the pro- 
jection and, indeed, every phase of their problems. The finished 
product is examined and changes are suggested. At times, the tele- 
graph and long-distance telephone are used when work would other- 
wise be delayed. Special services have been worked out in connection 
with plots and titles. We try to make it easy for members to ask for 
help by supplying them with cards upon which, by a pencil check, 
they may indicate their needs. We have worked with manufacturers 
of cine equipment in the development of new and the improvement 
of existing items. We have accepted the responsibility of representing 
both users and purveyors in international and in legislative matters. 
In all these, we serve individual amateurs, scientists, organizations, 
and business concerns, both large and small, for the same membership 
fee. Departments of the national governments of various countries, 
state units, national societies, and some of the greatest corporations 
in the United States use Amateur Cinema League services. 

As upon the professionals, color and sound descended upon us and 
brought a whole set of new complexities to be worked out which 
we had to face just as we were getting on our feet with a new technic 
of personal movie making. We have had to keep at least one jump 
ahead of our students in our information and training work and to 
keep a part of our mind fixed upon what would happen six months or 
a year ahead. We have been hounded by movie makers to persuade 
somebody to provide this or that item of equipment and we have 
tried to check demand against probable sale and to present reasoned 
recommendations to manufacturers. We have been faced with legisla- 
tive problems in many places, as old laws were rewritten and the 
revisions, just as the originals, took no account of non-theatrical 
problems or filmers. We had to face the difficulty of codes in the 
United States, under NRA, and to serve both users and purveyors 
in this complicated episode. We were able to be of some service in 
achieving a modification of the tariff law, in 1930, to permit free 
entry of personal films into the United States under certain restric- 
tions. It has been a pleasure for us to second the fine work of the 
Society of Motion Picture Engineers in attempting to establish unified 
motion picture standards for use in all countries and we pledge our 
continuance of support. 



Aug., 1936] THE AMATEUR CINEMA LEAGUE 217 

In relations with local groups and regional and national bodies, 
we have made no formal affiliations, nor have we asked dues from 
their local members or demanded obligations, although a number of 
such organizations have League membership. We have served clubs, 
as such, without charge. Our service is centralized, which we regard 
wise, but it carries with it no control or domination of those served. 
We have avoided commercialization of any League service or activity. 
We make no purchases or sales for members and do not favor dis- 
counts for them. We have been friendly with the industry supplying 
the tools of personal movie making but we have not subjected our- 
selves to its domination. It is worthy of note that this industry has 
"leaned over backward" in avoiding any appearance of wishing to 
control the policies of the League. We have not rendered special 
services for extra fees but have given all members what we had to 
offer them at a uniform membership rate. We have maintained an 
entire independence in the editorial policy of our publications. We 
have been careful to avoid premature and limiting definitions. As an 
example of this, we have steadfastly refused to define a film amateur, 
believing that the future of non-theatrical filming is so broad that a 
definition at this time would be absurd. We have not undertaken any 
tests of equipment or tried to place approval or disapproval upon any 
items presented. The one test is whether we permit an item to be 
advertised in our monthly publication, and, even there we do not 
indicate why we accept or reject. Our broad policy in this regard 
is to see that our magazine advertises only those objects or services 
that are believed by us to be practical and operable, and to offer 
a reasonable value at the price fixed. By now, we may lay claim to 
a few basic policies, although another might call them only prejudices. 
In our operations of all kinds, we try to remember that : 

(1) The future of non-theatrical filming is the joint concern of those who 
make equipment, of those who sell it, and of those who use it, and all these can 
work together successfully. 

(2) Service is more valuable to members than social reunions. 

(5) Technicalities that can not be translated into plain language are not simple 
enough for general use. 

(4) Whether he is a family filmer, a practical filmer, a scientist, or one who 
sells his film-making skill for profit, the League shall have something for every 
non-theatrical movie maker. 

(5) A service body is a poor place for organization politics. 

(6) Regimentation is the death of service. 

(7) An international body gets farther by friendship than by controversy. 



PHYSICAL TESTS ON CELLULOSIC FILMS, AND THEIR 
REPRODUCIBILITY* 

S. E. SHEPPARD, P. T. NEWSOME, AND S. S. SWEET** 

Summary. When all experimental errors of testing are adequately minimized, 
cellulose ester sheets show a dispersion of tensile strength values higher than that 
found for metal strips and wires. The dispersion of "yield point" values is much less 
than that of tensile strength. 

It is suggested that the lowest value (or, at any rale, the bracket of values lower 
than the average} of tensile strength for a number of tests equivalent to a given film 
length is a better measure of the probability of failure in performance than the average 
value. However, for comparative rating, it appears that generally the ratio of lowest 
to average is fairly constant. 

The physical tests discussed in this paper are general, in the de- 
termination of the strength of materials, whether metal, paper, cellu- 
losic, or similar films, used for photographic supports or packaging; 
or, again, rubber. Amplifications and variations of such tests are 
developed further which are intended to bring the tests into closer 
relation to specific practical requirements and durability in use. 

One of the chief difficulties in testing and development laboratories 
is the evaluation of individual strength tests in relation to performance 
tests. This is particularly the case when one is concerned not with 
the strength in relation to static loading, but in relation to cyclic 
dynamic loading under conditions simulating use. It is not the pur- 
pose to discuss this here, but to report upon some investigations as 
to the reproducibility of physical strength tests of cellulosic film sup- 
port materials. Since the strength of a chain is that of its weakest 
link, it is felt that neither a single value, nor an average value of a 
number of physical strength tests of a given material, can be a measure 
of the probability of failure in performance ; but that it is more rea- 
sonable to consider the lowest value of a number of tests equivalent to the 
working length in question as the significant strength figure. Rela- 

* Presented at the Fall, 1935, Meeting at Washington, D. C. Communica- 
tion No. 568 from the Kodak Research Laboratories. 
** Eastman Kodak Co., Rochester, N. Y. 

218 



TESTS ON CELLULOSIC FILMS 219 

lively, it may happen that as between different materials, these 
lower limit figures may be proportional to the average values for a 
sufficient number of tests but there is no a priori certainty about 
this ; it may be stated that statistics of the tests so far available indi- 
cate this to be generally true, but not invariably. 

That a number of tests should give values having a certain distribu- 
tion or dispersion is only to be expected the important thing is the 
extent of the dispersion, and its significance. Evidently, if the dis- 
tribution of values is very narrow, in other words, if the observations 
show a very small spread, and the reproducibility is high, the homo- 
geneity and uniformity are so also. In this respect the investiga- 
tion overlaps with the first part of one by Jones and Miles on the 
tensile strength of nitrocellulose films, 1 and it will be of interest 
to compare some of our results with theirs, particularly since we have 
also compared cellulose nitrate films with cellulose acetate. 

MATERIAL 

The material for the most part was prepared in the laboratory by a 
procedure to be described. Jones and Miles, in the investigation 
cited, compared films coated in the laboratory with two commercial 
film supports of cellulose nitrate. The latter showed a somewhat 
lower standard deviation,* from which it was concluded that 
the preparation in very large quantity might result in greater 
uniformity of local strain upon drying than in the smaller laboratory 
coatings. There is involved in this, however, both the manner of the 
laboratory coating and that of the manufacturing procedure. It 
does not appear, either from Jones and Miles' results or our own, that 
the differences between laboratory-prepared samples and regular 
products are very considerable in this respect. They are of interest to 
the manufacturer rather than to the user, to whom these results are 
chiefly presented. 

METHOD OF PREPARATION 

Jones and Miles used the method of coating upon a mercury 
surface of circular section. In the case of rather thin films, this 
tends to give a nearly isotropic sheet, free from directional strains, 2 
since the liquid surface allows a uniform retreat of the drying film. 
We have ourselves used a method of coating upon levelled glass plates, 

* Vide infra. 



220 



SHEPPARD, NEWSOME, AND SWEET [j. S. M. p. E. 



using a doctor-knife to adjust for a desired thickness. Films so 
coated are not isotropic McNally and Sheppard 2 showed that their 
properties tended to approach those of uniaxial crystals, but are 
sufficiently uniform either along or across the direction of flow and 
coating. Coating from acetone or acetone-methyl alcohol solution 
was carried out under standard conditions of humidity and tempera- 
ture, followed by precuring at 50C. and final curing at 100C., 
by which all but traces of solvent were removed. The samples were 
conditioned for 24 hours at 25C. and 45 per cent relative humidity 
before being tested. 

APPARATUS AND CONTROL 

The dynamometer used was of the Schopper type, previously de- 
scribed. 3 It has been shown by Sheppard and Carver 4 that films of 




FIG. 1. Showing dependence of yield point and breaking 
load of cellulose ester films upon rate of loading. 

cellulose esters are imperfectly elastic, and flow slightly even under 
very small loads. Consequently, the values of "yield point" and 
"breaking load" obtained depend upon the rate of loading, a result 
illustrated by Fig. 1, reproduced from Sheppard and Carver's paper. 
While yield points and breaking loads may be read from the auto- 
matic tracings, they may be obtained also from the sector scale of the 
pendulum weight, the former as the point at which the load first 
remains stationary,* the latter as the final value at break. It will 
be remembered that the "yield point" is simply the point at which the 
flow equals the rate of application of pull, but for a fixed speed it can 
be determined with good accuracy and is of value equal to, perhaps 
greater than, the "breaking load." In all the tests dealt with in this 
paper, the lower grip was moved at a speed of 8.6 cm. per minute. 

* Relatively. 



Aug., 1936] TESTS ON CELLULOSIC FILMS 221 

In order to check the performance of the instrument, a considerable 
number of tests was run upon metal wires and sheet-strips. These 
were of high uniformity of thickness, and overlapped the cellulose 
esters in regard to mechanical strength, as shown in Table I. With 

TABLE I 

Physical Constants of Metals Compared to Cellulose Acetate 







Tensile 


Young's 


Modulus of 


Bulk 






Strength 


Modulus 


Rigidity 


Modulus 


Metal 


Hardness 


(Kg. per 
Sq.Mm.) 


(Dynes per 
Sq. Cm.) 


(Dynes per 
Sq. Cm.) 


(Dynes per 
Sq. Cm.) 


Lead 


1.5 


2 


1.7 X 10" 


0.7 X 10 U 


0.75 X 10 11 


Tin 


1.5 


3 


5.0 


2.0 


5.0 


Cellulose Acetate 


2.0-2.5 


10 


0.3 


0.06 




Aluminum 


2.0 


18 


7.0 


2.5 


7.0 


Copper 


2.5 


28 


10.0 


4.2 


12.0 


Brass 


3.0-4.0 


100 


9.2 


3.7 


6.1 



copper wire No. 18 B&S gauge, 0.040 inch in diameter, an average 
breaking load of 19.0 kg. was found, with a maximum variation of 
1.5 per cent; a yield point of 18.0 kg., maximum variation 2.0 per 
cent; elongation, 39 per cent, maximum variation 12 per cent. Tin 
and lead foil also gave results of similar character. In general, as 
compared with the cellulosic materials, these metals and alloys showed 
considerably lower dispersion of the values for tensile strength and 
elongation. 

TEST PIECES AND PREPARATION 

The ultimate strength of many materials has been supposed to be 
greatly affected by the presence of cracks, even superficial cracks or 
scratches. Sheppard and Sweet 3 have shown that scratches upon 
the surface of film base affect the strength only inasmuch as they re- 
duce the thickness at that point. Briefer 5 has stated that "even a 
slight nick, so slight as to be imperceptible to the naked eye, will 
shorten the elongation curve 50 per cent or more." In confirmation 
of this, a nick of only 0.002 inch was found to produce a drop of 20 
per cent in strength and of 25 per cent in elongation. 6 In conse- 
quence, the method of shaping the test-pieces from larger sheets is of 
considerable importance. It has been established that cutting by 
shearing action with a knife (paper trimming board) is not as reliable 
as slitting with a special cutting edge. In the latter case, searing 
the edges of samples made no improvement in the reproducibility 



222 SHEPPARD, NEWSOME, AND SWEET [j. s. M. p. E. 

of tests, indicating that nicks which might start a tear were sub- 
stantially absent. 

In this connection, the length of the test-strip is of some importance. 
The probability of serious cracks or nicks being present in the edges 
will be proportional to the length of the strip. Examination of a 
series of different lengths gave a slightly higher mean value for the 
shortest, 2 cm., strip. 

Length Mean Tensile 

Strength (Kg.) 

2cm. 12.9 

5cm. 12.6 

10cm. 12.8 

15cm. 12.7 

In most of the tests described here a test-strip of 2 cm. between the 
grips was used. 

THICKNESS AND UNIFORMITY OF THICKNESS 

Experiments in this laboratory have shown that within the range 
significant for film support, strips of different thicknesses of the same 
material give identical tensile strengths per unit of cross-section. 
Hence, the actual breaking load of strips of the same width varies 
directly as the thickness. Jones and Miles, in the work referred to, 
have emphasized the importance of uniformity of thickness for uni- 
formity of behavior in tensile tests. In our experiments all thickness 
measurements (both original and at point of break) were made with 
a Federal thickness-gauge, reading to 0.0001 inch, which had been 
checked against an optical gauge. In addition, uniformity of thick- 
ness was further tested with an automatically recording gauge. The 
variations of thickness observed are illustrated in Table II, for three 
different materials. 

TABLE II 



Sheet 


Average 
Thickness 


Total 
Per Cent 
Variation 


Thickness 
at Break 


Total 
Per Cent 
Variation 


Acetate 1 
Acetate 2 
Nitrate 1 


0.00745 
0.00525 
0.00825 


1.3 

2.0 
1.2 


0.00655 

0.0045 
0.00735 


4.5 
4.4 
4.0 



It appears evident that the variation of tensile strength, deduced 
from reducing the breaking loads to values per sq. mm., is much 
greater than would be caused by variation in thickness and conse- 
quent error in apparent tensile value. 



Aug., 1936] 



TESTS ON CELLULOSIC FILMS 



223 



- L 



*.* ,? * 





224 



SHEPPARD, NEWSOME, AND SWEET [J. S. M. P. E. 



FREQUENCY POLYGONS AND DISTRIBUTION CURVES 

The data for tensile strength and elongation of the various types of 
material listed in Table III have been plotted as frequency polygons, 
and are shown in Figs. 2, 3, and 4. It was found that some of the dis- 
tributions were well represented by a symmetrical or Gaussian type 
of probability curve 



where h and k are constants. When x = 0, y = k; i. e. t the maximum 

ordinate. The value of /?, sometimes 
called "the measure of precision," is 
greater according as the curve is steeper 
in the neighborhood of the central or- 
dinate. 

Evidently, the distribution must be 
symmetrical with regard to higher and 
lower values of the deviations from the 
mean for this type to fit the observa- 
tions. An example is given in Fig. 5. 
The distribution is well fitted by taking 
k = 23, h = 0.075; for x = the 
average value is 13.25 kg. However, a 
number of the observations gave more or 
less "skew," or asymmetric distributions, 
the asymmetry being invariably in favor 
of, or "weighted" toward, the lower 
tensile bracket. The standard deviation 
of thickness was determined from a large 
number of measurements on the sup- 
ports used in the strength tests, with 




INQ LOAD IN K. 

FIG. 5. Probability curve of 
distribution. 



the following results: 

B type: Average thickness, 0.142 mm. (0.00558 inch) 

Standard deviation of thickness, 0.002 mm. (0.0008 inch) 
Standard deviation of thickness, 1.5 per cent 

These results should be compared with those given for the variation 
of tensile strength and elongation in Table III. 

AVERAGES 

The average values of tensile strength, yield point, and elongation 
are the arithmetical means of all the values. The average deviation 



Aug., 1936] 



TESTS ON CELLULOSIC FILMS 



225 



is the arithmetical mean of all the deviations from the average, irre- 
spective of sign. The standard deviation (S.D.) is the mean square- 
root of the squares of deviations from the mean. 

TABLE III 

Standard Deviation of Tensile Strength and Elongation 



Type 


Thickness 
(Approx.) 

(Mm.) 


Number 
of 
Values 


Tensile Strength 


Elongation 


Aver- 
age 

(Kg./ 
Mm.2) 


Standard 
Deviation 

(Kg./ 
Mm.*) 


Per Cent 
Standard 
Deviation 


Devia- 
Average tion 
(Per (Per 
Cent) Cent) 


Per Cent 
Standard 
Deviation 


Ai 


Acetate 


0.190 


200 


7.7 


0.76 


9.9 


65 


13.2 


20.3 


A, 


Acetate 


0.190 


100 


7.0 


0.31 


4.4 


73 


5.9 


8.1 


5i 


Acetate 


0.133 


100 


11.3 


0.90 


8.0 


48 


13.8 


28.5 


B 2 


Acetate 


0.133 


100 


10.0 


0.60 


6.0 


45 


5.4 


12.0 


C\ 


Nitrate 


0.203 


200 


12.9 


1.25 


9.7 






. . 


c, 


Nitrate 


0.133 


100 


11.1 


0.85 


7.6 


57 


8.5 


15.0 


c s 


Nitrate 


0.133 


100 


10.9 


0.67 


6.2 


52 


4.8 


9.2 


D 


Acetate 


0.127 


75 


9.4 


0.53 


5.6 


26 


4.7 


18.0 



Modal values of tensile strength, etc., are the values having the 
greatest frequency of occurrence in the frequency curves. 

Plots of log T (tensile) against frequency, and again of log T 




FIG. 6. Log tensile strength vs. 
frequency. 



FIG. 7. Log tensile strength vs. 
log frequency 



against log F (frequency) tended to give more symmetrical curves 
(Figs. 6 and 7). The latter plot, if parabolic, indicates a distribution 
function of the type 

y = j^-A'dog*-*)' 

which has been used successfully in the representation of the size- 
frequency distribution of precipitated particles and crystallites. 7 



226 



SHEPPARD, NEWSOME, AND SWEET [j. s. M. p. E. 



REPRESENTATIVE VALUES AND REPRODUCIBILITY 

It was stated in the introduction that the question be raised as to 
whether the average value of a tensile test was the most representative 
value for a material used in a film, or whether the lowest value ob- 

, __ , served should not be considered. 

Table IV shows that so far as the 
material examined goes, a large pro- 
portion show a fairly good propor- 
tionality between the average and the 
lowest values. 

The samples A 2 and Ci, which 
deviate most, were distinguished by 
A 2 having the most symmetrical, 
and Ci the most asymmetrical, or 
"skew," distribution. 



M 



03 



YIELD POINT 

The nature of the "yield point" 
and its dependence upon the testing 
conditions has already been discussed. 
It may be pointed out, however, 
that in practically all cases the dis- 
persion of values, as measured by 
the standard deviation, was much less 
than that of the breaking load, i. e., 
of tensile strength. This corresponds 
to the fact recognized in dealing with 
the strength of materials that the 
ultimate strength is affected by a 
variety of casual extrinsic factors. 
The narrower dispersion of yield point values is illustrated in Fig. 8. 



YIELD POINT IN k*. 

FIG. 8. Showing narrower dis- 
persion of yield point values. 



REPRODUCIBILITY, OR NUMBER OF TESTS REQUIRED FOR AVERAGE VALUE 
OF GIVEN ACCURACY 



The arithmetic mean of all the individual values in a given test 
(tensile strength, etc.) was obtained. The individual values were 
placed successively in groups of 5, 10, 20, 50, etc., in order of occur- 
rence, and the average value of each group recorded. It will be 
sufficient to summarize the conclusions. The average of five dupli- 



Aug., 1936] 



TESTS ON CELLULOSIC FILMS 



227 



TABLE IV 



Type 


Average 
Tensile 
Strength 

(Kg./Mm. 2 ) 


Lowest 
Tensile 
Strength 

(Kg./Mm.2) 


Highest 
Tensile 
Strength 

(Kg./Mm. ) 


Lowest value 


Average value 


Ai Acetate 


7.7 


6.1 


9.34 


0.80 


A 2 Acetate 


7.0 


6.5 


8.1 


0.93 


J5i Acetate 


11.3 


9.0 


13.1 


0.80 


B 2 Acetate 


10.0 


8.5 


11.2 


0.85 


C, Nitrate 


12.9 


9.7 


15.9 


0.755 


C 2 Nitrate 


11.1 


8.85 


12.8 


0.80 


C z Nitrate 


10.9 


9.1 


12.6 


0.83 


D Nitrate 


9.4 


8.2 


10.6 


. 0.87 



cate tests was found to give average deviations from the mean ranging 
from: 



2 . 7 to 4 . 5 per cent 

10. 5 to 24 percent 

8.7 to 12 percent 



Tensile 
Stretch 
Flexibility 



But the average deviation from the mean is not an adequate measure 
of accuracy, which is better expressed as the variation between mini- 
mum and maximum values. From this it is concluded that the aver- 
age of some 50 tests of tensile strength is necessary to be sure that 
differences of the order of 5 per cent are significant. 

REFERENCES 

1 JONES, G. G., AND MILES, F. D.: "The Tensile Strength of Nitrocellulose 
Films," /. Soc. Chem. Ind., 52 (Aug., 1933), No. 33, p. 251 T. 

2 McNALLY, J. G., AND SHEPPARD, S. E. i "Double Refraction in Cellulose 
Acetate and Nitrate Films," J. Phys. Chem., 34 (Jan., 1930), p. 166. 

3 SHEPPARD, S. E., AND SWEET, S. S. : "The Effect of Scratches on the Strength 
of Motion Picture Film Support," Trans. Soc. Mot. Pict. Eng. t VIII (1924), No. 
18, p. 102. 

4 SHEPPARD, S. E., CARVER, E. K., AND SWEET, S. S.: "The Time Factor and 
Yield Value of Cellulose Esters," Ind. Eng. Chem., 18 (Jan., 1926), p. 76. 

6 BRIEFER, M.: "Physical Properties of Motion Picture Film," Trans. Soc. 
Mot. Pict. Eng., VIII (May, 1924), No. 18, p. 177. 

6 SHEPPARD, S. E., AND SWEET, S. S. : "The Effect of Scratches and Cuts on the 
Strength of Motion Picture Film," Trans. Soc. Mot. Pict. Eng., IX (Oct., 1925), 
No. 24, p. 122. 

7 LOVELAND, R. P., AND TRIVELLI, A. P. H.: "Mathematical Methods of Fre- 
quency Analysis of Size of Particles. II. Application to Silver Bromide Pre- 
cipitates," /. Franklin Inst., 204 (Sept., 1927), No. 3, p. 377. 



COMMITTEES 

of the 
SOCIETY OF MOTION PICTURE ENGINEERS 

(Correct to July 20, 1936; additional appointments may be made at any time 
during the year as necessity or expediency may require) 



L. W. DAVEE 
A. S. DICKINSON 



ADMISSIONS 

T. E. SHEA, Chairman 
M. W. PALMER 
H. RUBIN 



H. GRIFFIN 
D. E. HYNDMAN 



O. M. GLUNT 
A. C. HARDY 



BOARD OF EDITORS 
J. I. CRABTREE, Chairman 



L. A. JONES 

G. E. MATTHEWS 



W. H. CARSON 
O. O. CECCARINI 



COLOR 

J. A. BALL, Chairman 
C. H. DUNNING 
R. M. EVANS 

A. M. GUNDELFINGER 



H. W. MOYSE 
A. WARMISHAM 



H. GRIFFIN 



H. BUSCH 

A. S. DICKINSON 

G. C. EDWARDS 



CONVENTION 
W. C. KUNZMANN, Chairman 

J. H. KURLANDER 

EXCHANGE PRACTICE 

T. FAULKNER, Chairman 
A. HIATT 
J. S. MACLEOD 



M. W. PALMER 



N. F. OAKLEY 
H. RUBIN 
J. H. SPRAY 



T. ARMAT 

G. A CHAMBERS 



A. N. GOLDSMITH 
A. C. HARDY 



HISTORICAL 

E. THEISEN, Chairman 
W. CLARK 



HONORARY MEMBERSHIP 

J. G. FRAYNE, Chairman 



G. E. MATTHEWS 
T. RAMSAYB 



H. G. TASKER 
W. E. THEISEN 



228 



E. HUSB 

K. F. MORGAN 



COMMITTEES OF THE SOCIETY 

JOURNAL AWARD 

A. C. HARDY, Chairman 



229 



G. F. RACKETT 
E. A. WILLIFORB 



J. CRABTREB 
R. M. EVANS 
E. HUSE 
T. M. INGMAN 



LABORATORY PRACTICE 

D. E. HYNDMAN, Chairman 
M. S. LESHING 
C. L. LOOTENS 
R. F. MITCHELL 



H. W. MOYSB 
J. M. NICKOLAUS 
W. A. SCHMIDT 
J. H. SPRAY 



MEMBERSHIP AND SUBSCRIPTION 

E. R. GEIB, Chairman 



Atlanta 

C. D. PORTER 

Boston 

T. C. BARROWS 
J. S. CIFRE 
J. R. CAMERON 

Camden & Philadelphia 
H. BLUMBERG 
J. FRANK, JR. 

Chicago 
B. W. DEPUE 
J. H. GOLDBERG 
S. A. LUKES 
R. F. MITCHELL 



Cleveland 
R. E. FARNHAM 
J. T. FLANNAGAN 
V. A. WELMAN 

Hollywood 
J. O. AALBERG 
L. E. CLARK 
G. H. GIBSON 
C. W. HANDLEY 

E. HUSE 

F. E. JAMES 

G. A. MITCHELL 
P. MOLE 

K. F. MORGAN 
G. F. RACKETT 

Minneapolis 
C. L. GREENE 



New York 

G. C. EDWARDS 

J. J. FINN 

G. P. FOUTB 

H. GRIFFIN 

W. W. HENNESSEY 

R. C. HOLSLAG 

M. D. O'BRIEN 

F. H. RICHARDSON 

H. B. SANTEE 

T. E. SHEA 

J. L. SPENCB 

J. H. SPRAY 

Rochester 

E. K. CARVER 

Washington 
N. GLASSER 

F. J. STORTY 



Australia 
H. C. PARISH 

Austria 

P. R. VON SCHROTT 

China 

R. E. O'BOLGER 



Canada 

F. C. BADGLEY 

C. A. DENTELBECK 

G. E. PATTON 



England 

W. F. GARLING 

R. G. LlNDERMAN 
D. McMASTER 

R. TERRANEAU 
S. S. A. WATKINS 



230 



COMMITTEES OF THE SOCIETY 



[J. S. M. P. E. 



France 
L. J. DIDIEE 
L. G. EGROT 
F. H. HOTCHKISS 
J. MARETTE 

Germany 

W. F. BIELICKE 

K. NORDEN 

Hawaii 

L. LACHAPELLE 



T. ARMAT 

H. T. COWLING 



O. B. DEPUE 



D. P. BEAN 
F. E. CARLSON 
W. B. COOK 
H. A. DEVRY 



India 

H. S. MEHTA 
L. L. MISTRY 
M. B. PATEL 

Japan 

T. NAGASE 

Y. OSAWA 

New Zealand 
C. BANKS 



Russia 

A. F. CHORINE 

E. G. JACHONTOW 

Travelling 

E. AUGER 

K. BRENKERT 

W. C. KUNZMANN 

D. McRAE 

O. F. NEU 

H. H. STRONG 



MUSEUM 

(Eastern) 

M. E. GILLETTE, Chairman 

G. E. MATTHEWS T. RAMSAYE 

E. I. SPONABLE 
(Western) 
E. THEISEN, Chairman 

J. A. DUBRAY A. REEVES 



NON-THEATRICAL EQUIPMENT 
R. F. MITCHELL, Chairman 
E. C. FRITTS 
H. GRIFFIN 
R. C. HOLSLAG 



J. H. KURLANDER 

E. Ross 
A. SHAPIRO 
A. F. VICTOR 



C. N. BATSEL 
L. N. BUSCH 
A. A. COOK 
L. J. J. DIDIEE 



PAPERS 

G. E. MATTHEWS, Chairman 
M. E. GILLETTE 
R. F. MITCHELL 
W. A. MUELLER 



H. B. SANTEE 
T. E. SHEA 

P. R. VON SCHROTT 

I. D. WRATTEN 



J. I. CRABTREE 
A. S. DICKINSON 



PRESERVATION OF FILM 
J. G. BRADLEY, Chairman 
R. EVANS 
C. L. GREGORY 
T. RAMSAYE 



V. B. SEASE 
W. A. SCHMIDT 



M. ABRIBAT 
L. N. BUSCH 
A. A. COOK 
R. M. CORBIN 
J. A. DUBRAY 



PROGRESS 

J. G. FRAYNE, Chairman 
R. E. FARNHAM 
E. R. GEIB 
G. E. MATTHEWS 
H. MEYER 
V. E. MILLER 



R. F. MITCHELL 
G. F. RACKETT 
P. R. VON SCHROTT 
S. S. A. WATKINS 
I. D. WRATTEN 



Aug., 1936] 



COMMITTEES OF THE SOCIETY 



231 



M. C. BATSEL 
J. I. CRABTREE 



J. O. BAKER 
T. C. BARROWS 

F. E. CAHILL 
J. R. CAMERON 

G. C. EDWARDS 
J. K. ELDERKIN 



PROGRESS AWARD 
A. N. GOLDSMITH, Chairman 



PROJECTION PRACTICE 

H. RUBIN, Chairman 
J. J. FINN 
E. R. GEIB 
A. N. GOLDSMITH 
H. GRIFFIN 
J. J. HOPKINS 
C. F. HORSTMAN 
P. A. McGuiRE 



C. DREHER 
J. G. FRAYNB 



R. MIEHLING 

E. R. MORIN 

M. D. O'BRIEN 

F, H. RICHARDSON 
J. S. WARD 

V. WELMAN 



PROJECTION SCREEN BRIGHTNESS 



A. A. COOK 
A. C. DOWNES 
D. E. HYNDMAN 



C. TUTTLE, Chairman 
W. F. LITTLE 
O. E. MILLER 
G. F. RACKETT 
H. RUBIN 



B. SCHLANGER 

A. T. WILLIAMS 
S. K. WOLF 



J. R. CAMERON 
J. J. FINN 



M. C. BATSEL 
L. E. CLARK 
F. J. GRIGNON 



PUBLICITY 

W. WHITMORE, Chairman 
G. E. MATTHEWS 

SOUND 

P. H. EVANS, Chairman 
K. F. MORGAN 
O. SANDVIK 
E. I. SPONABLE 



P. A. McGuiRE 
F. H. RICHARDSON 



R. O. STROCK 
H. G. TASKER 
S. K. WOLF 



F. C. BADGLEY 
M. C. BATSEL 
L. N. BUSCH 
W. H. CARSON 
A. CHORINE 
A. COTTET 
L. DE FEO 
A. C. DOWNES 
J. A. DUBRAY 
P. H. EVANS 



W. C. KUNZMANN 
J. H. KURLANDER 



STANDARDS 

E. K. CARVER, Chairman 
R. E. FARNHAM 
C. L. FARRAND 
H. GRIFFIN 
R. C. HUBBARD 
E. HUSE 
C. L. LOOTENS 
W. A. MACNAIR 
K. F. MORGAN 
T. NAGASE 



STUDIO LIGHTING 

R. E. FARNHAM, Chairman 
V. E. MILLER 
G. F. RACKETT 



N. F. OAKLEY 
G. F. RACKETT 
W. B. RAYTON 
C. N. REIFSTECK 
H. RUBIN 

0. SANDVIK 
H. B. SANTEE 
J. L. SPENCE 
A. G. WISE 

1. D. WRATTEN 



E. C. RICHARDSON 

F. WALLER 



232 COMMITTEES OF THE SOCIETY 

SECTIONS OF THE SOCIETY 
(Atlantic Coast) 

L. W. DAVEE, Chairman 
H. G. TASKER, Past-Chairman M. C. BATSEL, Manager 

D. E. HYNDMAN, Sec.-Treas. H. GRIFFIN, Manager 

(Mid-West) 

C. H. STONE, Chairman 

R. F. MITCHELL, Past-Chairman O. B. DEPUE, Manager 

S. A. LUKES, Sec.-Treas. B. E. STECHBART, Manager 

(Pacific Coast) 

G. F. RACKETT, Chairman 

E. HUSE, Past-Chairman K. F. MORGAN, Manager 
H. W. MOYSE, Sec.-Treas. C. W. HANDLEY, Manager 



FALL, 1936, CONVENTION 

ROCHESTER, NEW YORK 

SAGAMORE HOTEL 
OCTOBER 12-15, INCLUSIVE 



Officers and Committees in Charge 

PROGRAM AND FACILITIES 

W. C. KUNZMANN, Convention Vice-P resident 
J. I. CRABTREE, Editorial Vice-P resident 
G. E. MATTHEWS, Chairman, Papers Committee 
H. GRIFFIN, Chairman, Projection Committee 
E. R. GEIB, Chairman, Membership Committee 
W. WHITMORE, Chairman, Publicity Committee 
G. E. MATTHEWS, Chairman, Papers Committee 



G. A. BLAIR 

A. A. COOK 

J. I. CRABTREE 

K. M. CUNNINGHAM 



LOCAL ARRANGEMENTS 
E. P. CURTIS, Chairman 
K. C. D. HICKMAN 
L. A. JONES 
G. E. MATTHEWS 



I. L. NIXON 
W. B. RAYTON 
E. C. ROLAND 
L. M. TOWNSEND 



E. R. GEIB 



F. E. ALTMAN 
E. K. CARVER 



J. G. CAPSTAFF 
E. K. CARVER 



A. A. COOK 
W. H. REPP 



REGISTRATION AND INFORMATION 

W. C. KUNZMANN, Chairman 

S. HARRIS 

TRANSPORTATION 
C. M. TUTTLE, Chairman 

J. G. JONES J. C. KURZ 

H. B. TUTTLE 

HOTEL ACCOMMODATIONS 

K. M. CUNNINGHAM, Chairman 

A. A. COOK O. SANDVIK 

H. B. TUTTLE 

PROJECTION 

H. GRIFFIN, Chairman 

E. C. ROLAND E. F. TETZLAFF 

L. M. TOWNSEND 



233 



234 FALL CONVENTION [j. s. M. p. E. 

BANQUET 

I. L. NIXON, Chairman 

G. A. BLAIR R. M. EVANS S. E. SHEPPARD 

W. CLARK W. C. KUNZMANN H. B. TUTTLE 

A. A. COOK j. S. WATSON 

PUBLICITY 

W. WHITMORE, Chairman 

F. C. ELLIS J. C. KURZ G. E. MATTHEWS 

E. C. FRITTS E. C. ROLAND 

LADIES' RECEPTION COMMITTEE 

MRS. L. A. JONES, Hostess 

assisted by 

MRS. A. A. COOK MRS. C. M. TUTTLE MRS. H. B. TUTTLE 

MRS. R. M. EVANS MRS. S. E. SHEPPARD 

HEADQUARTERS 

The Headquarters of the Convention will be the Sagamore Hotel, where 
excellent accommodations are assured. A reception suite will be provided for 
the Ladies' Committee, which is now engaged in preparing an excellent program 
of entertainment for the ladies attending the Convention. 

Special hotel rates guaranteed to S. M. P. E. delegates, European plan, will 
be as follows: 

One person, room and bath $ 3.50 

Two persons, room and bath 6.00 

Parlor suite and bath, for two 10.00 

Parlor suite and bath, for three 12.00 

Room reservation cards will be mailed to the membership of the Society in 
the near future and everyone who plans to attend the Convention should return 
his card to the Hotel promptly in order to be assured of satisfactory accommo- 
dations. Registrations will be made in the order in which the cards are received. 
When the Sagamore Hotel is booked to capacity, additional accommodations will 
be provided by the Hotel Arrangements Committee at another hotel in the 
immediate vicinity of the Sagamore. 

A special rate of fifty cents a day has been arranged for S. M. P. E. delegates 
who motor to the Convention, at the Ramp Garage, near the Hotel. 

Golfing privileges may be arranged for any of the Convention delegates by 
consulting the Chairman of the Local Arrangements Committee. 

TECHNICAL SESSIONS 

An attractive program of technical papers and presentations is being arranged 
by the Papers Committee. Sessions and entertainment programs will be con- 
ducted at the Sagamore Hotel and at the plants of the Eastman Kodak Co. and 
the Bausch & Lomb Optical Co. in accordance with the tentative program which 
follows. 

The attention of authors is directed to an announcement of the Papers Com- 
mittee at the bottom of the inside cover of this issue of the JOURNAL. Those 



Aug., 1936 J FALL CONVENTION 235 

who contemplate submitting manuscripts for the Convention should communicate 
with the Papers Committee as promptly as possible. 

SEMI-ANNUAL BANQUET 

The Semi-Annual Banquet and Dance of the Society will be held at the Oak 
Hill Country Club on Wednesday, October 14th, at 7:30 P.M. Motor-coach 
transportation will be provided to and from the Club by the Transportation 
Committee. 

INSPECTION TRIPS 

Arrangements will be made on the days when the inspection tnps are conducted 
at the plants of the Eastman Kodak Co. and the Bausch & Lomb Optical Co. to 
transport the members to these plants. The members of the Society are also 
invited to be the guests of those companies at luncheon on those days. 

PROGRAM 
Monday, October 12th 

9:00 a. m. Sagamore Hotel Roof 

Registration 
Society business 

10:00 a. m.-12:00 m. Committee reports 

Technical papers program 

12:30 p. m. Sagamore Hotel Main Dining Room 

Informal Get-Together Luncheon for members, their 
families, and guests. Brief addresses by several 
prominent members of the industry. 

2:00 p. m.-5:00 p. m. Sagamore Hotel Roof 

Technical papers program. 

8:00 p. m. Eastman Theater 

"Color Photography" (with demonstrations and mo- 
tion pictures), Dr. C. E. K. Mees, V ice-President in 
Charge of Research, Eastman Kodak Co., Rochester, 

N. Y. 

Tuesday, October 13th 

9:00 a. m. Buses will be at the Sagamore Hotel to transport mem- 

bers and guests to the Kodak Research Laboratories 
at Kodak Park. 

10:00 a. m.-12:30 p. m. Technical papers program in the auditorium of the 
Kodak Research Laboratories. 



236 



FALL CONVENTION 



1 :00 p. m. 



Invitation luncheon at Kodak Park Works of Eastman 
Kodak Co. 



2:00 p. m.-5:00p. m. Inspection tour of Kodak Park and the Kodak Re- 
search Laboratories. 

The program for the evening of this day will be announced 
in a later issue of the JOURNAL. 



10:00 a. m.-12:00m. 



1 :00 p. m. 



Wednesday, October 14th 

Sagamore Hotel Roof 

Technical papers program. 

Invitation luncheon at Bausch & Lomb Optical Co. 
Transportation to the Bausch & Lomb plant will be 
provided. Buses will leave the Sagamore at 12:30 
P.M. sharp. 



2:00 p. m.-5:00 p. m. Inspection tour of the Bausch & Lomb plant. 

7:30 p. m. Oak Hill Country Club 

Semi-Annual Banquet and Dance of the S. M. P. E. : 
addresses and entertainment. Motor-coach trans- 
portation will be provided to and from the Club by 
the Transportation Committee. Coaches will 
leave the Hotel promptly at 7:00 P.M. 



Thursday, October 15th 

10:00 a. m.-12:00 p. m. Sagamore Hotel Roof 

Technical papers program 



2:00 p. m. 



Technical papers program 
Society business 
Adjournment of Convention 



APPARATUS EXHIBIT 

There will be no general apparatus exhibit because of the limited display space 
at the Convention headquarters. The Papers Committee, however, is arranging 
to hold the usual Apparatus Symposium, and would like to be notified of any 
papers for this session. 



SOCIETY ANNOUNCEMENTS 

BOARD OF GOVERNORS 

At a meeting held at the Hotel Pennsylvania, New York, N. Y., July 10th, fur- 
ther plans for the approaching Convention at Rochester were developed, as 
described elsewhere in this issue of the JOURNAL. In addition, reports rendered by 
O. M. Glunt, Financial V ice-President, indicated that the Society was in a fairly 
satisfactory financial condition, and that the membership was continuing to 
increase somewhat, although at a rate slower than that during the previous year. 

Nominations for officers for 1936 were completed, and ballots for voting upon 
these nominations will be mailed to the Active and Fellow membership of the 
Society the latter part of August. 

The question of the policies to be followed by the Sectional Committee on 
Motion Pictures, ASA, of which the SMPE is sponsor, was discussed at great 
length, and arrangements were made to send a delegate to the forthcoming meet- 
ing of the International Standards Association at Budapest, beginning August 
31st. At this meeting it is hoped that the long-continued differences as to 
16-mm. sound-film standardization will be reconciled, and thought will be 
given also to possible standardization in the 35-mm. field. 

FALL, 1936, CONVENTION AT ROCHESTER OCTOBER 12th-15th, 

INCLUSIVE 

Details concerning the approaching Convention at Rochester, beginning 
October 12th, will be found on page 233 of this issue of the JOURNAL, and at the 
foot of the inside front cover page. 

SOCIETY AWARDS 

At the meeting of the Board of Governors described above, reports were 
rendered by the Progress Award and the Journal Award Committees, nominating 
the recipients for these awards, which are to be granted during the approaching 
Convention at Rochester next October. Announcement of the names of the 
recipients will not be made before the Convention, but at that time a complete 
description of their accomplishments and contributions to the motion picture art, 
which form the bases for granting the awards, will be published. 

STANDARDS COMMITTEE 

At a meeting held at the General Office of the Society on July 17th, study was 
made of the group of new drawings of the Standards which have been prepared 
during the past several months. The new drawings will be submitted to the 
American Standards Association for approval, and will form the basis of the 
American presentations at the forthcoming conference of the International 
Standards Association at Budapest, beginning August 31st. 

237 



238 



SOCIETY ANNOUNCEMENTS 



[J. S. M. P. E. 



ADMISSIONS COMMITTEE 

At a recent meeting of the Admissions Committee, at the General Office of 
the Society, the following applicants for membership were admitted to the 
Associate grade: 



ANDERSON, J. A. 
Alexander Film 
Springs, Colo. 



Co., Colorado, 



ASHTON, H. 

3500 14th St., N. W., Washington 
D. C. 

BACH, W. 

431 Homestead Ave., Mount Vernon, 
N. Y. 

BONZGOV, V. 

Mazata str. 22/24, Apt. 2F, Lenin- 
grad, U. S. S. R. 

BOWERS, V. M. 

5508 S. Union Ave., Chicago, 111. 

BOYLE, W. E. 

1215 E. 18th Ave., Denver, Colo. 

BRAGG, H. E. 

38 N. Barnet St., East Orange, 
N.J. 

BRANDON, J. M. 

306 Georgia Ave., Lorain, Ohio. 

BYERS, J. K. 

11 Mount Felix, Walton-on-Thames, 
Surrey, England. 

CORTISSOZ, E. J. 

859 N. Las Palmas Ave., Hollywood, 
Calif. 

DAVIS, H. A. 

1437 Jackson Blvd., Chicago, 111. 

DAY, A. R. 

2033 N. Berendo St., Hollywood, 
Calif. 

DONALD, R. R. 

1022 Ninth St., N. W., Canton, Ohio. 

FONG, P. 

107 Des Voeux Road, Central Hong 
Kong, China. 



GORDON, V. H. 
459 W. 22d St., New York, N. Y. 

HALLIDAY, E. N. 

6982 Owen Ave., Chicago, 111. 

HENIUS, W. M. 

39 Byramjee Jeejibhoy Road, Bom- 
bay-Bandra, British India. 

HOUGH, G. W. 

1043 S. Olive St., Los Angeles, Calif. 

INNAMORATI, I. L. 

1, Piazza Indipendenza, Rome, Italy. 

IRELAND, P. 

481 Lake Ave., Rochester, N. Y. 

JACOBSEN, I. 

c/o Balaban & Katz Corp., 175 N. 
State St., Chicago, 111. 

JENNINGS, J. 

399 Fullerton Parkway, Chicago, 
111. 

KALMANSON, V. 

Leontievsky Pereulok dom 11, kv. 4, 
Moscow, U. S. S. R. 

KENNEDY, K. W. 

421 E. Maple Ave., La Grange, 111. 

KILLMAN, R. T. 

744 Benton Ave., Nashville, Tenn. 

KOJEVNIKOV, G. 

Lesnoy Propect, 37, Korpus 6, Apt. 
104, Leningrad, 100, U. S. S. R. 

KUSMIERZ, J. F. 

P.O. Box 203, Chicopee Falls, Mass. 

La Tart, L. 

118 Hatch St., Syracuse, N. Y. 

LATENER, L. 

Warner Bros., Earle Theatre Bldg., 
Philadelphia, Pa. 



Aug., 1936] 



SOCIETY ANNOUNCEMENTS 



239 



MARCUS, G. K. 

1923 81st St., Brooklyn, N. Y. 

MATHEWSON, W. 

Thief River Falls, Minn. 

O'BRIEN, W. S. 

353 W. Broadway, Waukesha, Wis. 

ODDIE, C. M. 

1064 Mills Bldg., San Francisco, 
Calif. 

PHILLIPS, R. G. 

2901 Paririe Ave., Chicago, 111. 

ROESSNER, C. H. 

Da-Lite Screen Co., 2723 N. Craw- 
ford Ave., Chicago, 111. 

SCHAEFER, E. J. 

5938 Lakepointe, Detroit, Mich. 

SCHWALBERG, A. W. 

16 Wilson Drive, New Rochelle, 

N. Y. 

SlCHELMAN, J. 

779 Riverside Drive, New York, 

N. Y. 



SOKOLOV, S. 

Lusinovskqya, 40, Apt. 19, Moscow, 

U, S. S. R. 

SORKIN, M. 

Nine Austin Park, Cambridge, Mass. 

STEPANIAN, A. M. 

Siratsky pereulok dom N116, Apt. 
186, Moscow 26, U. S. S. R. 

SWANSON, A. B. 

1152 N. Sycamore Ave., Hollywood, 
Calif. 

TOWNSLEY, M. 

4045 N. Rockwell St., Chicago, 111. 

TROLLOPS, E. R. 

430 S. Lincoln St., Casper, Wyo. 

VAN LEER, O. 

Carel Reinierszkade 299, The Hague, 
Holland. 

WlENKE, E. J. 

285 Forest Ave., Glen Ellyn, III. 



In addition, the following applicants have been admitted by vote of the 
Board of Governors to the Fellow and Active grades: 



CAHILL, F. E. (F) 
321 W. 44th St., New York, N. Y. 

BENDHEIM, E. McD. (M) 

19-22 22d Drive, Astoria, L. I. C., 
New York. 

McCoLLUM, A. B. (M) 

805 W. Lincoln St., Hoopeston, 111. 



PEREYRA, M. (M) 

O'Donnell, 41 Madrid, Spain. 

SCHUMACHER, E. W. (M) 

160 Fifth Ave., New York, N. Y. 

THRASHER, F. M. (M) 

100 Washington Sq., E., New York, 
N. Y. 



STANDARD S. M. P. E. 

VISUAL AND SOUND TEST REELS 

Prepared under the Supervision 

OF THE 
PROJECTION PRACTICE COMMITTEE 

OF THE 
SOCIETY OF MOTION PICTURE ENGINEERS 

c & 3 

Two reels, each approximately 500 feet long, of specially pre- 
pared film, designed to be used as a precision instrument in 
theaters, review rooms, exchanges, laboratories, and the like 
for testing the performance of projectors. The visual section 
includes special targets with the aid of which travel-ghost, 
lens aberration, definition, and film weave may be detected 
and corrected. The sound section includes recordings of 
various kinds of music and voice, in addition to constant- 
frequency, constant-amplitude recordings which may be used 
for testing the quality of reproduction, the frequency range 
of the reproducer, the presence of flutter and 60-cycle or 96- 
cycle modulation, and the adjustment of the sound-track. 
Reels sold complete only (no short sections). 

PRICE $37.50 FOR EACH SECTION, 
INCLUDING INSTRUCTIONS 

(Shipped to any point in the United States) 

Address the 

SOCIETY OF MOTION PICTURE ENGINEERS 

HOTEL PENNSYLVANIA 
NEW YORK, N. Y. 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXVII SEPTEMBER, 1936 Number 3 

CONTENTS 

Page 

A 13.6-Mm. Super-High-Intensity Carbon for Projection. . . . 
D. B. JOY 243 

Present Trends in the Application of the Carbon Arc to the 
Motion Picture Industry W. C. KALB 253 

Color Quality of Light of Incandescent Lamps 

R. E. FARNHAM AND R. E. WORSTELL 260 

Acoustic Considerations in the Construction and Use of 
Sound Stages D. P. LOYE 267 

A Unidirectional Microphone H. F. OLSON 284 

Harmonic Distortion in Variable- Density Records 

B. F. MILLER 302 

Stereoscopy on the Screen L. LUMIERE 315 

The Electron-Image Tube, a Means for Making Infrared 
Images Visible G. A. MORTON 321 

New Motion Picture Apparatus 

Copper-Oxide Rectifiers for Motion Picture Arc Supply. . . . 

I. R. SMITH 331 

Application of the Copper -Oxide Rectifier to Motion Picture 
Projection C. E. HAMANN 341 

Committees of the Society 348 

Fall, 1936, Convention at Rochester, N. Y., October 12-15, 
Inclusive 353 

Society Announcements 360 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors 
J. I. CRABTREE, Chairman 

O. M. GLUNT A. C. HARDY L. A. JONES 

G. E. MATTHEWS 



Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscriptions or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 

Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1936, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is 
not responsible for statements made by authors. 



Officers of the Society 

President: HOMER G. TASKER, Universal City, Calif. 

Past-President: ALFRED N. GOLDSMITH, 444 Madison Ave., New York, N. Y. 
Executive Vice-President: SIDNEY K. WOLF, 250 W. 57th St., New York, N. Y. 
Engineering Vice-President: LOYD A. JONES, Kodak Park, Rochester, N. Y. 
Editorial Vice-President: JOHN I. CRABTREE, Kodak Park, Rochester, N. Y. 
Financial Vice-President: OMER M. GLUNT, 463 West St., New York, N. Y. 
Convention Vice-P resident: WILLIAM C. KUNZMANN, Box 6087, Cleveland, Ohio. 
Secretary: JOHN H. KURLANDER, 2 Clearfield Ave., Bloomfield, N. J. 
Treasurer: TIMOTHY E. SHEA, 463 West St., New York, N. Y. 

Governors 

MAX C.- BATSEL, Front & Market Sts., Camden, N. J. 

LAWRENCE W. DAVEE, 250 W. 57th St., New York, N. Y. 

ARTHUR S. DICKINSON, 28 W. 44th St., New York, N. Y. 

HERBERT GRIFFIN, 90 Gold St., New York, N. Y. 

ARTHUR C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

EMERY HUSE, 6706 Santa Monica Blvd., Hollywood, Calif. 

GERALD F. RACKETT, 823 N. Seward St., Hollywood, Calif. 

CARRINGTON H. STONE, 205 W. Wacker Drive, Chicago, 111. 



See p. 348 for Technical Committees 



A 13.6-MM. SUPER-HIGH-INTENSITY CARBON FOR 
PROJECTION* 

D. B. JOY** 

Summary. A new 13.6-mm. super-high-intensity carbon is described which 
will burn at currents as high as 190 amperes and which has a higher intrinsic bril- 
liancy and a more uniform distribution of light across the crater face than the regular 
13.6-mm. carbon rated at 120 to 130 amperes. 

Tests comparing the light projected upon a projection screen by this new carbon 
and by the regular carbon show conclusively that the available light has been increased 
by at least 30 per cent. The arc lamp used with the carbons must be properly de- 
signed to take care of the increased current and carbon consumption. 



The regular 13.6-mm. high-intensity positive carbon burning at 
120 to 130 amperes and used in the condenser type of high-intensity 
lamp has been the light-source used in the largest theaters of the 
country for a number of years. The increase in general theater 
lighting, the size of the picture, the size of the theater, and the 
anticipated use of color have caused demands from a number of 
theaters for a 13.6-mm. high-intensity carbon that will furnish more 
light than is available from this standard carbon. 

In addition to this, in the last few years, background projection 
for process photography has been used extensively in motion pic- 
ture studios. This process, which has been described by Popovici, 1 
Harrison, 2 and others consists in projecting a picture of the desired 
background through a translucent screen and rephotographing this 
picture with foreground objects to give the final composite scene. 
Because of the light loss "occurring through the screen a very large 
amount of light is desired. It is also essential that the light-source 
have a considerable range of intensity because of the difference in 
density of the films being projected. A further requirement is that 
there should be a minimum decrease of light at the sides of the picture. 

It is therefore evident that both from the standpoint of projecting 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Laboratory, National Carbon Co., Inc., Fostoria, Ohio. 

243 



244 D. B. JOY [j. s. M. P. E. 

motion pictures and photographing motion pictures with projected 
backgrounds, it would be desirable to have available a light-source 
of the same dimensions as the present 13.6-mm. carbon but capable of 
giving a considerably greater amount of light and a more uniform 
distribution across the projection screen. 

The new super-high-intensity 13.6-mm. carbon has been designed 
to meet these requirements. It has the same outside diameter as the 
regular 13.6-mm. carbon but has a much larger core. Its design and 
composition are such that it will burn steadily at currents of 140 to 
190 amperes. At the lower current the crater is comparatively 
shallow, but at the higher currents it is considerably deeper than that 
of the regular carbon. 

The consumption of the carbon at various currents, compared with 
that of the regular 13.6-mm. carbon, is given in Table I. The maxi- 



TABLE I 

Consumption of Regular and Super 13.6-Mm. Carbons at Same Arc Setting 

Consumption 
Carbon Current Voltage (Inches per Hour) 

Regular 13.6-mm. 120 64 11.3 

Regular 13.6-mm. 130 68 15.5 

Super 13.6-mm. 140 60 12.6 

Super 13.6-mm. 160 66 18.0 

Super 13.6-mm. 180 72 25.5 



mum current-carrying capacity of the regular carbon is 130 amperes. 
In contrast to this, the super-high-intensity carbon gives a very 
steady light at much higher currents and consumption rates than 
the regular carbon. It can be anticipated, because of the larger core 
size and higher consumption, that the intrinsic brilliancy would be 
both higher and more uniformly distributed across the crater face 
than in the case of the regular 13.6-mm. carbon. 

Measurements of the intrinsic brilliancy across the crater face are 
given in Fig. 1. The curves show that at 180 amperes the intrinsic 
brilliancy of the super-carbon crater is noticeably higher than that of 
the regular carbon crater at its maximum current of 130 amperes. 
It is also evident that with the super-carbon the tapering of the in- 
trinsic brilliancy from the center to the sides of the crater is less. 
For example, at a distance of 3 millimeters from the center, the 



Sept., 1936] A 13.6-MM. SUPER-HIGH-INTENSITY CARBON 



245 



intrinsic brilliancy compared with the brilliancy at the center has 
decreased to 69 per cent for the regular carbon at 130 amperes, but 
only to 82 per cent for the super-carbon at 180 amperes. This flat- 
ness of the intrinsic brilliancy curve of this new carbon is accentuated 
at the lower current densities. At 160 amperes the intrinsic brilliancy 
at the center of the crater is a little lower than that of the regular car- 
bon at 130 amperes, but is considerably higher at the sides of the 
crater. The total crater diameter increases with increasing current. 
The significance of this difference in the intrinsic brilliancy dis- 
tribution becomes apparent upon comparing magnified images of the 




6.0 SO +.0 J.O 



/.O O 1.0 2.0 JiO +.O O 6.O 

//y MM. 



FIG. 1. Distribution of intrinsic brilliancy across crater face of 
regular and super 13.6-mm. high-intensity carbons. 



crater face of the regular carbon and of the super-carbon. With the 
regular carbon there is a noticeable change in the color of the light 
near the edge of the crater, where the incandescent shell is the pre- 
dominating light-giving material. With the super-carbon, ap- 
parently, the incandescent gases fill the crater more completely, re- 
sulting in much less change of color near the edge of the crater and a 
greater diameter where the gases themselves form the principal 
source of light. 

These intrinsic brilliancy curves indicate that the new carbon when 
burned at its rated current should give a higher light and more uni- 



246 



D. B. JOY 



[J. S. M. P. E. 



form light upon the projection screen than the present carbon. This 
is more apparent if the amount of light is calculated for given areas of 
the heart or central portion of the crater. This comparison is given 
in Fig. 2, which shows the total candle-power emitted directly in 
front of the arc for the various central areas of the crater. For ex- 
ample, if an area at the heart of the crater of 8 millimeters in diameter 
is considered, the candle-power emission for the regular 13.6-mm. car- 
bon at 130 amperes is 28,700 and for the super-carbon at 180 amperes 
is 38,400. If an optical system utilizes this area it means that the 
light through the optical system would be proportional to the candle- 




FIG. 2. Candle-power directly in front of arc, of central areas 
of crater of regular and super 13.6-mm. high-intensity carbons. 



power, or about 34 per cent greater for the super-carbon. The light 
upon the screen from the regular and the super-high-intensity 13.6- 
mm. carbons was measured by means of the optical system shown 
in Fig. 3a. This system consists of the regular or super-carbon, a 
pair of condensing lenses, a standard sound aperture plate, and a 
5 l /2-inch, //2.5 objective lens. The condensers were designed to give 
an elliptical shape to the spot on the aperture plate. A shutter was 
not used in the system. 

The position of burning of the carbons is shown in Fig. 3b. The 
same burning position was used in all tests with this optical system 



Sept., 1936J A 13.6-MM. SuPER-HlGH-lNTENSITY CARBON 



247 



in order to avoid any difference 3 in light or light distribution caused 
by a change in either the position of the carbons or the arc flames. 
The light upon the projection screen was measured by means of 
Weston photronic cells corrected by means of a green screen to 
approximate the sensitivity of the eye. These cells were placed at 
the positions shown in Fig. 3c. The cells at the sides and corners 
were placed at the edges of the light zone; and their readings, com- 
pared with the reading of the center cell, give a true picture of the 
decrease in the light from the center to the sides or corners of the 
screen. 

Preliminary measurements showed that the super-carbons give 
an increase in light when the positive carbon is held at exactly the 
same position with respect to the optical system, and also tend to 




FIG. 3. (a) Optical system used in tests; (b) positions of car- 
bons and arc; (c) location of phototronic cells on projection 
screen. 



build up the light at the sides of the screen. This, of course, would 
be anticipated from the shape of the intrinsic brilliancy curves. In 
order to place the measurements upon a common basis, it was de- 
cided to take a series of readings of the screen light, moving the lenses 
with respect to the aperture plate and carbons. By this method the 
distribution of light falling upon the projection screen could be 
varied over a considerable range, and the light from the two types of 
carbon could be compared directly for the same light distribution. 
Screen light measurements were made of the regular carbon at 120 
and 130 amperes and of the super-carbon at 160 and 180 amperes. 
These measurements were all grouped according to the light dis- 
tribution upon the screen and were then plotted as shown in Fig. 4. 
In this figure the total lumens projected to the screen are plotted 



248 



D. B. JOY 



[J. S. M. P. E. 



against the distribution. This gives a direct comparison of the 
amount of light obtained from these carbons at the various cur- 
rents and for the distributions noted in the figure. For example, 
for a distribution factor from the center to the sides of 80 per cent, 
and from the center to the corners of 60 per cent, the regular car- 
bon at 130 amperes provides 5700 lumens on the screen and the 
super-carbon at 180 amperes 7500 lumens. These values, and, to 
some extent, the distribution of the light, depend upon the design of 
the optical system 4 ' 5 ' 6 as well as upon the light from the arc; but 




tfNTEK. 100 IOO 100 

j/Z^J 84- 32 SO 

coeneeses 63 so 



7B 



IOO /OO /OO 

76 74- 72 

tt.s 53 so.s 



/OO 
70 



FIG. 4. Light on projection screen for various distributions of the 
light (shutter of optical system not running). 



since the same optical system was used for all these measurements, 
the figures are directly comparable. It is evident that the super- 
carbon at either 160 or 180 amperes affords a distinct increase in 
light over the regular carbon at its highest rated current of 130 
amperes. This advantage holds for the light distributions com- 
monly encountered. 

These data emphasize the necessity of making comparative mea- 
surements upon the basis of the same light distribution on the screen. 
The effect of the distribution is better illustrated by Fig. 5 which 



Sept., 1936] A 13.6-MM. SUPER-HIGH-INTENSITY CARBON 



249 



shows the foot-candle readings on a screen 15 X 20 ft. for the super- 
carbon at 180 amperes, for various light distributions with the opti- 
cal system that has been described. The foot-candles are plotted 
against the distance from the center of the screen as illustrated by 
the diagram in the lower right-hand corner. For a distribution fac- 
tor of 80 per cent at the sides of the screen, values are shown of 30 
foot-candles at the center, 24 at the sides, and 18 foot-candles at the 
corners. If the distribution factor is 72 per cent at the sides, the 



44 
40 
36 

* 



" 



2 



U 



oo- 

00 



oo 



C t yr# <s/i E cy#Mie 



-a* 



ao 



7.'. 



*3 







s 



t/.a 



//.a 



FIG. 5. Effect of light distribution upon foot-candle reading on 15 
Y^ 20-ft. projection screen (shutter of optical system not running). 



foot-candle reading at the center is 43, at the sides 31, and at the 
corners 22, and the total lumens upon the screen are increased from 
7500 to 10,300. Cook 4 and Rayton 5 have pointed out that the 
effect of the complete optical system, when adjusted to give maxi- 
mum light output, is to emphasize the contrast in intensity between 
the center and the edges of the screen. It is possible, however, by 
readjusting the focus, to compensate for this effect so that the light 
at the sides and corners is satisfactory. It is evident from Fig. 4 that 
for the light distributions actually measured in these tests the maxi- 



250 



D. B. JOY 



[J. S. M. P. E. 



mum light had not been obtained. However, the curves do cover 
the range used in actual projection, particularly at the left-hand por- 
tion of the figure. A decrease of light to 80 per cent at the sides of 
the screen is not uncommon. Fig. 6 and Table II show a comparison 
of the foot-candle readings and lumens on a 15 X 20-ft. screen for 
the same screen light distribution for the regular and the super-high- 
intensity carbons. These foot-candle readings as well as the total 
lumens again show definitely the gain in light made possible by the 
super-carbons. 

If it is desired to build up the light at the sides and the corners of 




FIG. 6. Foot-candle readings on 15 X 20-ft. screen for distribu- 
tion factor of 100 at center, 80 at sides, and 60 at corners (shutter 
of optical system not running). 

the screen, compared with the center, it can be done by means of this 
super-carbon. For example, by proper focusing and with the same 
optical system, the super-carbon at 180 amperes will project the 
same amount of light to the center of the screen, but approximately 
10 per cent more light to the sides and 20 per cent more to the corners, 
than the regular carbon at 130 amperes. 

From the foregoing intrinsic brilliancy curves and comparisons 
on the screen with a conventional optical system, it is evident that 
the super-carbon will provide at least 30 per cent more light than the 
regular carbon for the same screen light distribution. In order to 
utilize the new carbon to the best advantage the lamp must be cap- 



Sept., 1936] A 13.6-MM. SuPER-HlGH-lNTENSITY CARBON 251 

able of withstanding the high currents, and the feeding mechanism 
must feed the carbons uniformly at the rates indicated in Table I. 

The more uniform intrinsic brilliancy distribution across the 
crater face of the super-carbon may make it possible to use an optical 
system having lower magnification and still obtain an even greater 
increase in light than has been obtained with the optical system used 
in this work. This has been approximated to a limited extent in 
the tests summarized in Fig. 4 by moving the lenses so as to give the 
same light distribution for the regular carbon and the super-carbon. 

TABLE II 

Total Lumens on Screen for Light Distribution of 80 Per Cent at Sides and 60 Per 

Cent at Corners 

(No Shutter Running) 

Per Cent 

Carbon Current Lumens Lumens 

Regular 13.6-mm. 120 4550 100 

Regular 13.6-mm. 130 5700 125 

Super 13.6-mm. 160 6750 148 

Super 13.6-mm. 180 7500 165 

REFERENCES 

1 POPOVICI, G. G.: "Background Projection for Process Cinematography," 
/. Soc. Mot. Pict. Eng., XXIV (Feb., 1935), No. 2, p. 102. 

2 HARRISON, H.: "Problems of Background Projection," Amer. Cinemat. 
(Jan., 1934), p. 353. 

3 JOY, D. B., AND DOWNES, A. C.: "Some Causes for Variations in the Light 
and Steadiness of High-Intensity Carbons," /. Soc. Mot. Pict. Eng., XVI (Jan., 
1931), No. 1, p. 61. 

4 COOK, A. A.: "A Review of Projector and Screen Characteristics, and 
Their Effects upon Screen Brightness," /. Soc. Mot. Pict. Eng., XXVI (May, 
1936), No. 5, p. 522. 

6 RAYTON, W. B.: "The Effect of Aperture Lenses upon Illumination," J. 
Soc. Mot. Pict. Eng., XXIII (Dec., 1934), No. 6, p. 309. 

6 HARDY, A. C.: "The Optics of Motion Picture Projectors," /. Soc. Mot. 
Pict. Eng., XIV (March, 1930), No. 3, p. 309. 

DISCUSSION 

MR. BRENKERT: How much would you have to adjust the optical system to 
reduce the light from the super-carbon to what is supplied by the regular carbon? 
What is the effect at the center of the screen? 

MR. JOY: Referring to Fig. 4, when adjusting for equal distribution the screen 
lumens for both the regular and the super-carbon will fall upon the same vertical 
line. The super-carbon must be moved about 0.1 inch farther from the lens to 



252 D. B. JOY 

obtain the same ratio of light at the sides to light at the center of the screen; 
that is, the same distribution. 

If the carbons were burned in exactly the same position, the super-carbon might 
have a distribution factor of, say, 100 at the center and 80 at the sides of the 
screen, while the regular carbon would give factors of 100 at the center and 74 at 
the sides. If the super-carbon is moved from the lens until the same distribution 
of light occurs on the screen as with the regular carbon in the original position, 
the amount of light will be greater, as shown in Fig. 4. 

MR. BRBNKERT: If you have a reading at the corners of the screen of, for ex- 
ample, 14 foot-candles for the regular carbon, and adjust the super-carbon to 
produce at least the same reading at the corners, what would be the reading at 
the center? 

MR. JOY: It would increase by considerably more than 30 per cent; perhaps 
40 or 50. 

MR. BRENKERT: Was that actually demonstrated by the same optical system? 

MR. JOY: Yes. Assume that we have a ratio of light at the center to light at 
the sides of 100 to 80, as is the case in Fig. 6. The regular carbon at 130 amperes 
with a given optical system on a 20-ft. screen gives 23 foot-candles at the center 
and 18 at the sides; whereas the super-carbon at 180 amperes and moved slightly 
back from the rear condenser to give the same distribution with this optical system, 
gives 30 foot-candles at the center and 24 at the sides, and the total light increase 
is 30 per cent. 

If we move the super-carbon toward the rear condenser, the light at the center 
and at the sides of the screen will decrease, faster at the center than at the 
sides, and the distribution will become even flatter. If, on the other hand, we 
move the super-carbon farther from the rear condenser, the light at the sides and 
the center increases, again faster at the center than at the sides, at least in 
the range that we investigated as shown by Figs. 4 and 5. For example, with the 
super-carbon moved back so that the distribution factor at the sides is 76, 
the foot-candle reading is 37 at the center and 28 at the sides, or an increase of 
50 to 60 per cent over the regular carbon at 130 amperes and for a different light 
distribution. 



PRESENT TRENDS IN THE APPLICATION OF THE CARBON 
ARC TO THE MOTION PICTURE INDUSTRY* 



W. C. KALB** 



Summary. The present trend in the motion picture industry is toward more ex- 
tensive use of the high-intensity carbon arc in both the theater and the studio. From 
the earliest days, progress in the industry has been attended by constant demands for 
more light and for light of better quality. The high-intensity arc is the most effective 
means of satisfying these demands, and promises in a short time to dominate the 
field of theater projection and to extend its field of application in studio lighting. 



PROJECTION 

The necessity for using, in projection, a light-source of very high 
intrinsic brilliancy is illustrated by the following example. A 
screen image 20 feet wide is 90,000 times the area of the 0.800-inch 
aperture through which the light is projected, and with a magnifica- 
tion of 6:1 from the crater to the aperture, is 3,240,000 times the 
area of that portion of the light-source focused within the aperture 
limits. Disregarding all losses in pick-up and transmission, an 
intensity of 10 foot-candles incident upon the screen calls for a 
brightness of 111 candles/mm. 2 at the source. A 120-degree mirror 
picks up only about 75 per cent of the total light emitted by the 
source. Losses through the film and the lens further reduce the 
intensity of illumination of the screen. It is therefore obvious that 
screen sizes now in use have gone well beyond the limit at which the 
low-intensity arc with a maximum intrinsic brilliancy of 175 
candles/mm. 2 can provide a satisfactory level of screen illumina- 
tion. 

Low-Intensity Arcs. The properties of the low-intensity reflecting 
arc have been discussed in this JOURNAL by Joy and Downes. 1 There 
is a definite limit both to the intrinsic brilliancy and to the whiteness 
of the light available from this source, fixed by the subliming tempera- 
ture of carbon. Dr. Chaney and his associates 2 have determined the 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** National Carbon Company, Inc., Carbon Sales Division, Cleveland, Ohio. 

253 



254 W. C. KALB [j. s. M. P. E. 

maximum brightness temperature of the positive crater of the carbon 
arc as being approximately 3810K., and their findings have been 
confirmed by other investigators. Fig. 1 shows the energy distribu- 
tion curve of the low-intensity carbon arc operated with 12-mm. 
positive and 8-mm. negative carbons at 30 amperes, 55 volts, d-c.; 
and, for comparison, the theoretical curve of black body radiation at 
3810K. It is apparent from these curves that, with the exception 
of the peaks at approximately 2500 and 3900 A, which are character- 
istic of all carbon arcs, the energy distribution from this arc is a close 
approximation to the theoretical limit. The maximum intrinsic 
brilliancy under the conditions defined is slightly less than 175 
candles/mm. 2 

High-Intensity Arcs. The high -in tensity arc is not subject to the 
same limitations as the low-intensity arc. Introduced to the motion 
picture industry more than 15 years ago, it has been described and 
its characteristics discussed in several papers in this JOURNAL. 3 - 4>5 
The high-intensity arc is operated at much higher current-densities 
in the electrodes than is the low-intensity arc. The positive carbon 
burns with a deep crater and is provided with a central core containing 
rare-earth minerals. The vapors from this core, confined by the arc 
stream to the cup-like crater, attain a brilliancy far greater than 
that associated with the temperature at which carbon sublimes. 
The result is a snow-white light and a crater brilliancy much higher 
than that attainable in the low-intensity arc. In the larger high- 
intensity arcs, the brilliancy of the crater exceeds 800 candles/mm. 2 
From Fig. 2, which shows the energy distribution of a typical high- 
intensity arc, it is evident that the colors are more evenly balanced 
and the light consequently whiter than that of the low-intensity 
arc. 

The larger theaters were prompt to make use of the greater volume 
and improved quality of light that the high-intensity arc provided. 
However, its use for projection in small theaters was not practicable, 
from an economic standpoint, up to 3 or 4 years ago. The first impor- 
tant extension of the high-intensity principle of arc operation came 
with the development of the a-c. high-intensity carbon, 6 ' 7 ' 8 which 
was shortly followed by the Suprex carbon 9 a similar carbon de- 
signed for direct current. Both these new carbons are copper coated 
and of smaller diameter than the carbons previously used in high- 
intensity arcs. They are operated without being rotated, and are 
gripped at a point remote from the arc. Prompt development of 



Sept., 1936] CARBON ARC IN MOTION PICTURE INDUSTRY 



255 




2000 



eooo 

AN6STROM UNITS 



ULTRA-VIOLET 



FIG. 1. Energy distribution from low-intensity arc: (solid line) 
30-ampere, 55-volt, d-c. arc; 12-mm. positive carbon; (dotted line) 
radiation curve of theoretical black body at 3810K. 



ULTRA-VIOLET 



I VIOLET BLUE GREEN YEtLOW ORANGE 



FIG. 2. Energy distribution from high-intensity arc: 125-ampere, 
63-volt, d-c. arc; 13.6-mm. positive carbon. 



256 W. C. KALB [j. s. M. P. E. 

lamps for their use placed high-intensity light-sources for the first 
time within the economic reach of the small theater. 

Advantages of High-Intensity Projection. The experience of 
theaters that have used high-intensity projection has demonstrated 
that it possesses two distinct advantages. First, the snow-white 
quality of the screen illumination has proved much more pleasing to 
the audience than the somewhat yellow tint characteristic of the low- 
intensity arc. Second, the higher level of general illumination per- 
mitted by the increased screen brightness adds greatly to the comfort 
of the patrons entering the theater. These advantages are rapidly 
extending the use of the high-intensity arc in the smaller theaters, 
displacing the low-intensity, reflecting arc which, in recent years, has 
practically monopolized this field. 

The Super-High-Intensity Arc. For some time there has been a 
demand by a number of the larger theaters for still greater screen 
illumination than can be supplied by the 13.6-mm. high-intensity arc 
operated at 120-130 amperes. Screens well over 40 feet wide are now 
being used in some theaters. Since the intensity of screen illumina- 
tion from a given volume of projected light varies inversely as the 
square of the image width, it is apparent, from the example cited 
earlier, that these large screens require a light-source of tremendous 
power. 

This latest demand for more projection light has been met by the 
development of a 13.6-mm. super-high-intensity carbon, described by 
D. B. Joy. 10 This carbon is adapted to steady operation over a cur- 
rent range of 140 to 190 amperes. At the upper range of current it 
provides 30 per cent more light than the regular 13.6-mm. high- 
intensity carbon at 130 amperes. There is also a more uniform dis- 
tribution of brilliancy over the crater face of the new carbon, with a 
resultant improvement in the distribution of light upon the 
screen. 

Improvements in Lamps. In addition to the improvements in car- 
bon electrodes, there have been notable improvements in projection 
lamp design during the last few years. Among these are improved 
feeding mechanisms, closer control of the arc position, magnetic 
stabilization of the arc stream, and increase in light pick-up. Old 
type low-intensity lamps pick up a cone of illumination about 45 
degrees in extent. The low-intensity reflecting arc increased the 
angle of collection to 106 to 120 degrees. Reflecting types of high- 
intensity arc use mirrors having collection angles of 95 to 122, and 



Sept., 1936] CARBON ARC IN MOTION PICTURE INDUSTRY 257 

condenser types, 69 to 79 degrees. The smaller angles of pick-up in the 
latter are to some extent compensated by lower ratios of magnifica- 
tion. The latest lamps, designed for the new a-c. high-intensity and 
Suprex carbons are using mirrors picking up light over angles as great as 
145 degrees. The optics of projection place limits upon the extent to 
which this trend toward greater angles of pick-up can be carried. 
The improvements that have been made, however, have been a sub- 
stantial factor in making higher intensities of screen illumination 
available. 

STUDIO LIGHT 

In the field of production, as well as in projection, substantial 
progress is being made in adapting the carbon arc to present needs. 
The development of the studio carbon arc, using metal-coated white- 
flame carbons, has already been discussed. 11 ' 12 Although essentially 
a flame type of arc, the broadside studio arc is operated under condi- 
tions quite different from those applying to the regular white-flame 
photographic carbon arc. The improved lamp design eliminates all 
lamp noises and fulfills every demand of sound picture production. 
At the usual operating current of 35 to 45 amperes, the V2-inch 
regular white-flame photographic carbon carries a current-density 
of 180 to 200 amps. /in. 2 , whereas the current-density in the metal- 
coated carbons of the studio arc at 35 to 40 amperes is 450 to 515 
amps. /in. 2 . This is comparable to the current-density in many high- 
intensity arcs. While this new studio arc can not be defined as a high- 
intensity arc, because it lacks the well defined crater and the char- 
acteristic gas-ball of the latter, the character of the light emitted 
differs materially from that of the regular white-flame carbon, as may 
be seen in Fig. 3. In quality of light this studio arc has many of the 
characteristics of the high-intensity arc. Its photographic effective- 
ness and its excellent color balance for monochromatic as well as for 
color productions have been discussed in papers by Bowditch and 
Downes. 13 ' 14 

Sun arcs and rotary spots using the high-intensity arc have been 
greatly improved to adapt them to the sound stage. A new high- 
intensity rotary spot of compact design 15 combines the ideal beam 
characteristic of the condenser type lamps with the high power of the 
reflecting arcs. By means of an improved optical design, which 
includes the use of a modified Fresnel type of condensing lens, this 
lamp makes use of a much higher percentage of the total light from the 



258 



W. C. KALB 



[J. S. M. P. E. 



source than the older condenser lens designs. This design entirely 
eliminates the often-troublesome shadow of the negative carbon and 
its support, and provides a range of beam-spread from a 4-degree 
spot beam to a 44-degree flood, without dark spot or rings. Regard- 
less of spread, the highest intensity of the beam is always at the 
center, falling off smoothly toward the edges. Such a beam can very 
easily be blended with the beams from adjacent lamps. The carbons 
are fed continuously, maintaining uniform arc voltage and arc gap, 
so that the arc burns without change of intensity or color. The 



7 



ANGSTROM UHITS 



ULTRA-VIOLET 



YELLOW ORAN6C 



FIG. 3. Energy distribution from photographic carbons: (full 
line) 8-mm. metal-coated white-flame studio carbons, 40 amperes, 
37.5 volts d-c.; (dotted line) 13-mm. regular white-flame photo- 
graphic carbons, 35-amperes, 37.5 volts d-c. 

carbon-feeding mechanism has been made sufficiently silent to permit 
operating the lamps at normal speed within 10 feet of the micro- 
phones. 

The new super-high-intensity arc is rapidly rinding application in 
the studio for background projection, in which the increased volume 
of illumination is of distinct advantage. There is further advantage 
in the wide range of current over which steady operation obtains, 
permitting adjustment of the projection light to compensate for a 
wide variation of density in the film projected upon the background 
screen. Upon the basis of increased light output, as well as perfect 
color balance of the light, the adaptation of the super-high-intensity 
arc to stage illumination in motion picture production likewise seems 
to be indicated. 

REFERENCES 



1 JOY, D. B., AND DOWNES, A. C.: "Properties of Low-Intensity Reflecting 
Arc Projector Carbons," /. Soc. Mot. Pict. Eng. t XVI (June, 1931), No. 6, p. 684. 



Sept., 1936] CARBON ARC IN MOTION PICTURE INDUSTRY 259 

2 CHANEY, N. K., HAMISTER, V. C., AND GLASS, S. W.: "The Properties of 
Carbon at the Arc Temperature," Trans. Electrochem. Soc., LXVII (1935), p. 201. 

3 BASSETT, P. R.: "The High-Power Arc in Motion Pictures," Trans. Soc. 
Mot. Pict. Eng., IV (1920), No. 11, p. 79. 

*BENFORD: "High-Intensity Arc," Trans. Soc. Mot. Pict. Eng., IX (1925), 
No. 24, p. 71. 

6 JOY, D. B., AND DOWNES, A. C.: "Characteristics of High-Intensity Arcs," 
/. Soc. Mot. Pict. Eng., XIV (March, 1930), No. 3, p. 291. 

6 JOY, D. B., AND DOWNES, A. C.: "A New Alternating-Current Projection 
Arc," J. Soc. Mot. Pict. Eng., XXI (Aug., 1933), No. 2, p. 116. 

7 JOY, D. B., AND GEIB, E. R.: "Operating Characteristics of the High- 
Intensity Alternating- Current Arc for Motion Picture Projection," /. Soc. Mot. 
Pict. Eng., XXIII (July, 1934), No. 1, p. 27. 

8 JOY, D. B., AND GEIB, E. R.: "The Relation of the High-Intensity A-C. 
Arc to the Light on the Projection Screen," /. Soc. Mot. Pict. Eng., XXIII (July, 
1934), No. 1, p. 35. 

9 JOY, D. B., AND DOWNES, A. C.: "Direct-Current High-Intensity Arcs 
with Non-Rotating Positive Carbons," /. Soc. Mot. Pict. Eng., XXII (Jan., 
1934), No. 1, p. 42. 

10 JOY. D. B.: "A 13.6-Mm. Super-High-Intensity Carbon for Projection." 
Presented at the Spring, 1936, Meeting at Chicago, 111, J. Soc. Mot. Pict. Eng., 
XXVII (Sept., 1936), No. 3, p. 243. 

11 JOY, D. B., BOWDITCH, F. T., AND DOWNES, A. C.: "A New White-Flame 
Carbon for Photographic Light," J. Soc. Mot. Pict. Eng., XXII (Jan., 1934), 
No. 1, p. 58. 

12 MOLE, P.: "A New Development in Carbon Arc Lighting," /. Soc. Mot. 
Pict. Eng., XXII (Jan., 1934), No. 1, p. 51. 

13 BOWDITCH, F. T., AND DOWNES, A. C.: "The Photographic Effectiveness of 
Carbon Arc Studio Light-Sources," /. Soc. Mot. Pict. Eng., XXV (Nov., 1935), 
No. 5, p. 375. 

14 BOWDITCH, F. T., AND DOWNES, A. C.: "The Radiant Energy Delivered 
on Motion Picture Sets from Carbon Arc Studio Light-Sources," /. Soc. Mot. 
Pict. Eng., XXV (Nov., 1935), No. 5, p. 383. 

" MOLE, P.: "A Super-Powered Arc Spot Light," Internal. Phot., VII (Nov., 
1935), No. 10, p. 22. 



COLOR QUALITY OF LIGHT OF INCANDESCENT 
LAMPS* 



R. E. FARNHAM AND R. E. WORSTELL** 

Summary. The advantages of concentrating the source of gas-filled incandescent 
lamps are discussed, and the various forms available and their application to optical 
systems and reflectors are shown. 

Data regarding the temperature (color and maximum) of the various types of 
lamps are presented, and the similarity of the radiation of incandescent lamps to 
that of a Planckian radiator of suitable temperature is indicated. Curves showing 
the amount of light emitted at various wavelengths or colors for all lamps of interest to 
the motion picture industry are presented, in terms of both equal visual output and 
equal wattage. A discussion of the energy in the ultraviolet region and the effect of 
glass bulbs and lenses concludes the paper. 

Years ago the color quality of light was of no importance in most 
motion picture photography. With the old orthochromatic emul- 
sions, light-sources of radically different color characteristics were 
mixed indiscriminately upon a set. With the introduction of pan- 
chromatic film sensitive to all wavelengths in the visible spectrum, 
some attention 1 began to be paid to the color characteristics of the 
light-source. Today, with the diversity of types of "black-and-white" 
emulsions, the ever-increasing use of color photography, the recog- 
nition of ultraviolet light in some applications, and the complexity of 
processing methods, the spectral energy characteristics of light- 
sources employed in the industry are of vital importance. 

Much has been published in various scientific and research journals 
regarding the spectral energy distribution of incandescent lamps. 
However, the data are abstruse, and it is therefore the purpose of this 
paper to present the subject in a form readily usable by motion 
picture engineers. 

Extensive researches by Forsythe, Worthing, 2 and others have 
shown that the radiation from an incandescent tungsten source is 
continuous from the near ultraviolet, through the visible portion of 
the spectrum, and well into the infrared region. They have found 



* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** General Electric Co., Nela Park, Cleveland, Ohio. 



260 



COLOR QUALITY OF INCANDESCENT LAMPS 



261 



also that it follows very closely the radiation characteristics of the 
hypothetical black body or Planckian radiator. If the temperature 
of an incandescent lamp is known, the black body radiation curve 
for that temperature as determined by Planck's formula shows 
fairly accurately the energy distribution of the lamp. Temperature 
measurements of lamp filaments are generally given either as "maxi- 
mum" or "average." The 
maximum temperature is 
usually midway between 
the supports and at the 
center coils. Support 
and lead-in wires pro- 
duce cooler zones in 
several turns of the coil 
either side of the point 
where they contact the 
filament. Forsythe has 
found, however, that for 
the majority of filament 
constructions employed 
in lamps in the 110-120- 
volt range, the maximum 
temperature corresponds 
very closely to the color 
temperature ; sufficiently 
so that the values of 
maximum temperature 
may be used in choosing 
the Planck radiation 
curve. 3 Table I gives 
the maximum true tem- 
peratures in degrees Kel- 
vin of a number of typical lamps of interest to the motion picture 
industry. 

The curves of Fig. 1 show the spectral energy distribution for color 
temperatures ranging from 2600 to 3500 K. These are representative 
of a series of lamps operating at the temperatures indicated, and have 
been drawn in the conventional manner through a common point, 
viz., 100 per cent relative energy at 5600 A. These data are presented 
in 100-degree steps rather than for each lamp temperature, which in 




5000 5SOO 



FIG. 1. Spectral energy distribution in the 
visible region from tungsten filaments drawn 
arbitrarily for equal radiation intensities at 
wavelength 5600 A. 



262 



R. E. FARNHAM AND R. E. WORSTELL [J. S. M. p. E. 



some cases changes by only 5, to avoid confusion arising from 
crowding the curves at the shorter wavelengths. To obtain the 
energy distribution in the visible spectrum of any of the lamps listed 



Maximum True 


TABLE I 

Temperatures of Several Types of Incandescent 


Lamp 

Maximum 


Lamps 


Watts Volts 


Efficiency 
(Lumens/- 
Bulb Watt) 


Rated True 
Av. Life Temperature 
(Hrs.) (Degrees K.) 


General Service 


60 115 


A -21 


12.5 


1000 


2755 




100 115 


A -23 


15.2 


750 


2835 




200 115 


PS-30 


17.0 


1000 


2880 




300 115 


PS-35 


18.1 


1000 


2905 




500 115 


PS-40 


19.4 


1000 


2935 




1000 115 


PS-52 


20.7 


1000 


3000 




1500 115 


PS-52 


21.7 


1000 


3020 


Studio 


IOOOMP 115 


PS-52 


24.5 


250 


3130 


Set Lighting 


1500MP 115 


PS-52 


26.0 


250 


3180 




2000 MP 115 


G-48 


27.5 


100 


3225 




5000MP 115 


G-64 


29.0 


100 


3280 




10000MP 115 


G-96 


29.5 


100 


3300 


(Movieflood) 


2000CP 115 


PS-52 


32.7 


15 


3380 




2000CP 115 


G-48 


32.7 


25 


3370 




5000OP 115 


G-64 


32.7 


75 


3370 




10000CP 115 


G-96 


32.7 


75 


3370 


Projection 


300 115 


T-10 


23.5 


25 


3230 


(Monoplane) 


500 115 


T-20 


26.3 


50 


3265 




900 30 


T-20 


26.5 


100 


3240 


Projection 


500 115 


T-10 


25.0 


25 


3295 


(Biplane) 


750 115 


T-12 


26.0 


25 


3255 




1000 115 


T-20 


27.6 


25 


3260 


Photocell 7 


. 5 amps. 10 








3165 


Exciter 4 


amps. 8.5 








3060 


Photoflood No. 1 


250 115 


A -21 


33.5 


2 


3490 


Photoflood No. 2 


500 115 


A -25 


33.5 


6 


3430 


Photoflood No. 4 


1000 115 


PS-35 


33.5 


10 


3410 


Photoflash 










3500* 



in Table I it is necessary merely to interpolate between the two 
curves of temperature in Fig. 1 nearest the temperature of the 
lamp in question. 

As the efficiency of a filament is raised or lowered, the temperature 
changes accordingly, as does the light output and wattage. It is also 
true in the case of lamps of equal wattage that the light emitted 

* Average color temperature. 



Sept., 1936] COLOR QUALITY OF INCANDESCENT LAMPS 



263 



varies in quantity as well as in color quality, depending upon the 
filament temperature. To illustrate, in Fig. 2 are shown the spectral 
distributions of energy in the infrared, visible, and ultraviolet regions 




WAVE LENGTH -ANGSTROM UNITS 
4000 8000 12000 16000 20OOO 3400O 28000 320OO 36000 40000 44000 48000 

FIG. 2. Total spectral energy distribution from tungsten filaments of 
equal wattage but different temperatures. 

emitted by two tungsten filaments at 3500 and 2600K., as computed 
by Holladay 4 from data on Plane kian radiators. Each filament con- 
sumed the same wattage, and the two filaments therefore were 
radiating equal total 
energy. It will be ob- 
served that as the tem- 
perature increases so does 
the percentage of total 
radiation emitted in the 
visible and ultraviolet, 
with some decrease in 
the infrared. It is also 
apparent that radiation 
at the shorter wave- 
lengths has increased in 
greater percentage than 
that at the longer wave- 
lengths below 7000 A, 
thereby resulting in a 
color change. In Fig. 3 
the visible region of Fig. 2 
has been shown to a 
larger scale, and for 



WAVE LENGTH -ANGSTROM UNITS 



3500'K 

3400 

3300 

3200 

3100 

3000 

2900 



6SOO 7000 



FIG. 3. Spectral energy distribution in the 
visible region from tungsten filaments of equal 
wattage but different temperatures. 



264 



R. E. FARNHAM AND R. E. WORSTELL [J. S. M. P. E. 





3000 3500 4000 

FIG. 4. Spectral energy distribution in the 
ultraviolet from tungsten filaments of equal 
wattage but different temperatures. 

three commonly used types of bulb glass, 
of Fig. 4 corrected for the trans- I00r _ r _ 
mission characteristics of lime 
glass such as is used for the 
Photoflood and Movieflood 
lamps. Since similar data for 
lead glass vary less than the 
width of the line in the chart 
from those given for lime glass, 
Fig. 6 is applicable to lead glass 
as well. Similarly, Fig. 7 shows 
the data for Pyrex glass as used 
with the 2-, 5-, and 10-kw. lamps 
employed for motion picture 
studio photography. Attention 
is called to the fact that Fig. 4 
is plotted to an ordinate scale 



* Data from B. T. Barnes, Lamp 
Development Laboratory, General 
Electric Company, Nela Park, Cleve- 
land, Ohio. 



purposes of comparison, 
curves at 100 K. inter- 
vals have been included. 
Due to recent develop- 
ments in recording sound 
it is of importance to 
study the amount of 
energy emitted in the 
ultraviolet by incandes- 
cent lamps at several 
temperatures. These 
data are presented in 
Fig. 4 with no allowance 
made for the transmis- 
sion of the bulb glass in 
the near ultraviolet. 
Fig. 5* gives the trans- 
mission characteristics in 
the ultraviolet region for 
Fig. 6 presents the data 



WAVE LENGTH -ANGSTROM UNITS 



2800 3000 3200 3400 3600 3800 4000 

FIG. 5. Transmission per millimeter 
of thickness of three types of glass in 
the ultraviolet. 



Sept., 1936] COLOR QUALITY OF INCANDESCENT LAMPS 



265 






ANGSTROM UNITS 





NGSTROM UNITS 



FIG. 6. Spectral energy distri- 
bution in the ultraviolet from 
tungsten filaments of equal wat- 
tage but different temperatures, 
through lime glass 1 mm. thick. 



3000 3500 4000 

FIG. 7. Spectral energy distri- 
bution in the ultraviolet from 
tungsten filaments of equal wat- 
tage but different temperatures, 
through Pyrex glass 1 mm. thick. 



I VIOLET I BLUE I GREEN JYELLOWlORANGtl RED 



140 



120 



five times more open and an abscissa scale two times that employed 
in Fig. 3. However, the numerical values of relative energy are 
directly comparable. 

It has become quite 
common practice to use 
the No. 1 Photoflood 
lamp in conjunction with 
the standard A, B, and 
5-C tricolor filters for pro- 
ducing three-color sepa- 
ration negatives. Fig. 8 
shows the relative radiant 
energy available in each 
color when each of the 
three filters is employed 
with the Photoflood 
lamp. 

Color processes, such 
as Dufaycolor, Koda- 
chrome, and Techni- 
color, require substan- 
tially white light for correct color reproduction. For these processes 
the correct color quality can be obtained by using Coming's Lunar 




7000 



FIG. 8. Spectral energy distribution from 
Photoflood lamp No. 1, transmitted through A, 
B, and C-5 tricolor filters. 



266 



R. E. FARNHAM AND R. E. WORSTELL 



White No. 570 filter with a Photoflood lamp or a lamp operating 
at essentially the same color temperature as the Photoflood. The 
resulting light output from this combination is shown in Fig. 9. 
Libby-Owens-Ford medium-blue and Brigham's No. 26 gelatin pro- 
duce practically the same result. 

REFERENCES 

1 FARNHAM, R. E.: "The Effective Application of Incandescent Lamps for 
Motion Picture Photography," Trans. Soc. Mot. Pict. Eng., XII (1928), No. 34, 
p. 464. 

2 FORSYTHE, W. E., AND WoRTHiNGTON, A. G. i "The Properties of Tungsten 
and the Characteristics of Tungsten Lamps," Astro phy. J., LXII (April, 1925), 
No. 3, p. 146. 

3 Miscellaneous Publication No. 56, U. S. Bureau of Standards, Washington, 
D. C. 

4 HOLLADAY, L. L.: "Proportion of Energy Radiated by Incandescent Solids 
in Various Spectral Regions," /. Opt. Soc. Amer. and Rev. Sci. Instr., 17 (Nov., 
1928), No. 5, p. 329. 



VIOLET I BLUE I GREEN IvELLOWlORANGE! 



DISCUSSION 

MR. MILI: The authors show a table giving the maximum temperature of 
various incandescent filament lamps. In addition, a temperature of 3500K. 

is given for the photoflash lamp. 
While it is true that the color 
temperature of an incandescent 
tungsten lamp is about the same 
as the maximum temperature, 
this is not true for the photo- 
flash lamp. According to the 
latest tests, 3500 K. is the average 
color temperature of the photo- 
flash throughout the whole cycle 
of the flash, and not the maxi- 
mum temperature, which is 
doubtless much higher. 

MR. WORSTELL: Mr. Mili is 
correct. The color-temperature 
shown for the photoflash lamp is 
an average and not a maximum 
value. The maximum color tem- 
perature occurs when the flash 
reaches its peak. Since the peak 
endures for only a few thou- 















^ 
















s^ 












>x^ 






100 

eo 

60 








/ 


_ 






5 






Q^ 








1 




*$ 


r 








w 




3E- 










5 


^ 


i^ 






/ 




Jji 


z 








y 






/ 








/ 




2 




01 






/ 






/ 


_CORN, 5 


y^ 


^Sn 


^FLOOQ. 


X 




^-^ 














o 


















WAVE LENGTH - ANGSTROM UNITS 




400C 1SOO 5000 WOO 6000 6SOO 7000 



FIG. 9. Spectral energy distribution from 
Photoflood lamp No. 1, transmitted through 
Corning Lunar- White No. 570 filter. 



sandths of a second, the color temperature at this point is very difficult to 
obtain. I know of no one who has determined it. 



ACOUSTIC CONSIDERATIONS IN THE CONSTRUCTION 
AND USE OF SOUND STAGES* 



D. P. LOYE** 

Summary. Sound insulated stages are required for the production of sound pic- 
tures. Stages required to house a number of sets should be made acoustically dead. 
Stages consisting of only one set, such as scoring stages used for recording music, 
should have acoustical characteristics comparable to those of the concert hall. 

A scoring stage should not only have the proper reverberation time-frequency char- 
acteristic but, in addition, the wall and ceiling surfaces should be broken up in order to 
diffuse the sound. Measurements made on a stage where sound reflection from the 
floor was not prevented indicated the effect upon the frequency characteristic of a 
prominent first reflection. 

The use of more than one microphone for pick-up may lead to difficulties comparable 
to those experienced with stages having prominent reflection. Characteristic charts 
showing these effects are discussed in the paper. Rules, based upon the preliminary 
experimental work described, are given for avoiding poor quality where it is deemed 
necessary to use more than one microphone for pick-up. 

Before the days of sound recording, the director supervised the 
actions of his cast by means of a megaphone. The stages upon which 
he operated were regarded as satisfactory if they were rain-proof. 
The noise of the arc lights did not interfere with making the picture. 
To soothe the nerves of actors and actresses, offstage orchestras were 
often employed. 

Upon the introduction of sound, the technic was of necessity 
changed, and sound-proof stages were constructed. The director was 
forced to abandon the megaphone, the lights were required to be 
noiseless, and offstage music could no longer be used. Part of the 
need for the orchestra was obviated by eliminating the extraneous 
noises that formerly had served to annoy the actors and actresses. 

STAGE INSULATION 

Some of the first sound stages to be constructed were expensive. 
Neither the required insulation nor the exact design data for obtain- 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Electrical Research Products, Inc., Hollywood, Calif. 

267 



268 D. P. LOYE [j. s. M. P. E. 

ing specific degrees of insulation were known. Heavy double-wall 
construction was adopted, the stages consisting essentially of a room 
within a room, the inner structure being isolated as completely as pos- 
sible from the outer. Studies and experience have indicated that by 
properly balancing the studio traffic and the cost of the stage con- 
struction, sound pictures can be recorded economically on stages that 
are appreciably less expensive than those originally built. It is still 
necessary in many instances to provide double-walled stages, but 
lighter materials are now employed and the cost of construction is 
appreciably less than originally. By properly combining the various 
kinds of acoustic materials, high insulation can still be attained when 
required. 

A question that very naturally arises in connection with the con- 
struction of a sound stage is, how much insulation is required. The 
answer can be found by determining the maximum noise level that 
can be permitted within the stage, and the level of the outside noises, 
which must be prevented from disturbing the recording. 

The maximum noise level permitted under the average conditions 
of recording in Hollywood studios is approximately 30 db. above the 
reference standard of 10~ 16 watts/cm. 2 , as measured with a sound- 
level meter having a 30-db. equi-loudness contour weighting charac- 
teristic. A 1000-cycle tone having an intensity of zero db. is slightly 
lower than the threshold of audibility of the average ear. This maxi- 
mum permissible level corresponds roughly to the noise of footsteps 
upon a carpet ten feet away, or to the noise produced by the average 
person when breathing, heard from a distance of two or three feet. 

The noise levels that will exist outside the completed stage will, of 
course, vary somewhat with the particular studio conditions. If the 
stage is to be built at the edge of a studio lot, for instance, near a 
street upon which there is considerable traffic, the noise will be more 
severe and less subject to control than it would be if the stage were 
constructed near the center of the lot. Building a stage adjacent to 
a busy thoroughfare makes it necessary to provide greater insulation, 
involving heavier and more expensive construction. 

Measurements recently made preparatory to building a new stage 
indicated that when the studio traffic was unrestricted, the noise in- 
tensity on the stage site ranged from 70 to 88 db. above the reference 
level. Inasmuch as traffic was subject to control during recording 
periods, the noise from a nearby woodworking mill having a maximal 
intensity at the stage site of 75 db. was the most important noise to 



Sept., 1936] ACOUSTICS IN CONSTRUCTION OF STAGES 269 

be excluded. To prevent this noise from reaching a value on the stage 
in excess of 30 db. above the reference level, the stage was required to 
have an insulation of 45 db. Measurements made following the com- 
pletion of the stage indicated that the insulation adequately fulfilled 
this requirement. 

The stage was of the double-wall type, the two wall sections being 
supported by separate studs. The floor and ceiling provided insula- 
tion consistent with that of the walls. Double doors, well sealed, 
were required to provide insulation in keeping with that provided by 
the walls. It was necessary to close both parts of each double door 
tightly in order to avoid leaks and maintain the proper noise reduc- 
tion. Measurements indicated that failure to observe this precaution 
resulted in a marked increase in the noise in the portions of the stage 
adjacent to the doors. In order to prevent the transmission of traffic 
rumbles to the stage, the foundation was separated from the street 
pavement by a moat of soft earth and from ramps leading to the 
street by soft plastic filler. 

STAGE REVERBERATION 

Although proper acoustic insulation of sound stages is very im- 
portant, it is not the only requirement. Satisfactory sound recording, 
for instance, could not be carried on in a barn-like stage even though 
the stage were well insulated. The reverberation would be too great. 
The question of what reverberation time-frequency characteristics 
should be provided can be answered by considering, first, the purposes 
that the stages serve. 

Sound stages are generally used for housing a number of sets, each 
one representing a scene or scenes from portions of a picture. Inas- 
much as the sets vary widely in character, it is reasonable to assume 
that the accompanying sounds would vary in acoustical quality. 
The most satisfactory recording conditions exist when the acoustical 
characteristics of the set are comparable to those of the room or other 
location in which the action is represented as taking place, some 
changes being necessary to allow for the present monaural character 
of the microphone pick-up technic. Sets depicting outdoor scenes 
should not be reverberant. A scene occurring in a small room can not 
be best recorded upon a stage having the reverberation of a large live 
room. It would have been quite unnatural if, in the picture Skippy, 
Jackie Cooper's bathroom monolog on the tyrannical practice of par- 
ents who insist that their little sons wash their teeth, had been re- 



270 D. P. LOYE [j. s. M. P. E. 

corded as if the action had taken place in Carnegie Hall. The illusion 
under such circumstances would not have been compatible with the 
private character of Skippy's tooth-brush-moistening act. 

It is evident that a sound stage can not readily be made to provide 
the variety of acoustical effects appropriate to the various kinds of sets 
to be constructed upon it. The varying characteristics, if provided, 
must be contributed by the acoustical characteristics of the sets and 
by the placement of the microphone. It is therefore desirable that the 
stage be acoustically inconspicuous. In other words, the stage should 
be made as dead as possible; inasmuch as no part of it is seen in the 
completed picture, it should not be heard. 

To accomplish this, it was common practice in constructing the 
original sound stages to fill the space between the studs with rock- 
wool. The thickness of the rock- wool fill ranged from 4 to 8 inches, 
depending upon the dimensions of the studs used in constructing the 
inner wall. The present recommended practice is to use either a 
4-inch rock-wool fill, or a 2-inch rock-wool blanket over the studs, 
leaving an air space between the blanket and the surface behind it. 
Both the rock-wool fill and the 2-inch blanket over the studs provide 
good low-frequency absorption, which is desirable in order to guard 
against boominess on the stage. Stages so constructed have virtually 
flat reverberation time-frequency characteristics, the time through- 
out generally being less than one second. 

The high absorption of the walls and ceiling, desirable for reducing 
stage reverberation to a minimum, also reduces the noise level of dis- 
turbances within the stage as well as those transmitted through the 
walls from the outside. The higher the acoustic absorption of the 
inner surfaces of the stage, the more completely will noises be elimi- 
nated. 

SCORING STAGE CHARACTERISTICS 

The stages that have been described so far are used for housing 
several sets. It is evident, however, that in some cases only one set 
is desired on a stage. In such instances the stage becomes the set, 
although the latter term is hardly applicable where photographing is 
not done. The most common form of single-set stage is the scoring 
stage used for making musical recordings. Such stages should be 
relatively live, rather than dead. They are often used for recording 
opera or other performances depicted as occurring in large theaters or 
concert halls. Scoring stages should, therefore, have acoustical char- 
acteristics comparable to those of the concert hall. 



Sept., 1936] ACOUSTICS IN CONSTRUCTION OF STAGES 



271 



The optimal reverberation time for scoring stages employing the 
current recording methods has been discussed by Stanton and Schmid 1 
in a paper in which are given data on the optimal reverberation time 
of broadcasting and recording studios as established by years of ex- 
perience. The limits discussed by these authors are shown by the 
curves of Fig. 1. 

In determining these optimal reverberation data, consideration was 
given to an important difference existing between listening conditions 
and present pick-up conditions of recording. It is an experimental 



20 



*4 



.a 2 

IM 



-3 o.e 



" 



0.4 



0.2 



0.0 

f 




4 i 

100000 

Volume in cubic feet 



1000000 



FIG. 1. Scoring stage optimal reverberation time. 

fact that the loudness sensation is independent of the difference in 
phase between the sound pressures at the two ears of a listener. If, 
for instance, the two ears are stimulated by sound pressures of the 
same frequency, the loudness is the same regardless of whether the 
pressures are in or out of phase. As a result, the effects upon a normal 
listener of irregularities in the acoustic pattern of an auditorium are 
minimized, and, as Wente has pointed out, 2 the apparent liveness of 
the sound perceived by a listener is appreciably less than the recorded 
liveness. This effect can be observed by listening first with the two 
ears, and then observing the increase of apparent liveness that occurs 
when one ear is stopped. Inasmuch as the present recording technic 



272 D. P. LOYE [j. S. M. P. E. 

is monaural in character, even though multiple microphones may be 
used, scoring stages should be so designed and used that the liveness 
of musical recordings when reproduced under optimal conditions will 
be natural rather than accentuated. It is common practice to accom- 
plish this by increasing the acoustic absorption in the scoring stage 
above what would be required for optimal direct listening conditions 
by placing the microphone closer to the orchestra than the listener 
would be located, and by distributing a major portion of the acoustic 
absorption at the end of the stage where the microphone is located. 

The above-described limitations can be overcome to a large degree 
by stereophonic recording and reproduction. Such recordings involve 
the use of two separate recording channels, the two microphones used 
in picking up the sound being separated by an appreciable portion of 
the width of the auditorium. Reproduction requires the use of sepa- 
rate reproducer, amplifier, and loud speaker systems, the loud speakers 
being placed upon opposite sides of the stage. The details of the re- 
producing system used for direct musical reproduction have been fully 
described. 3 

Experimental stereophonic recordings were made by engineers of 
Electrical Research Products, Inc., during May and June of 1933, of 
organ, solo, and choir music in the Church of the Blessed Sacrament 
at Hollywood. Two separate microphones were placed above the 
audience section of the. church, and separate equalized lines trans- 
mitted the music to two separate amplifier and recording systems at 
the test laboratory of Electrical Research Products, Inc. Reproduc- 
tion of these recordings by means of two separate reproducer, ampli- 
fier, and loud speaker systems indicated the very marked improve- 
ment achieved by the method. Better "presence," depth, and a 
marked improvement in quality and naturalness were evident. 

It is important to consider not only the optimal amount of acoustic 
treatment in designing a scoring stage, but also the most effectual dis- 
tribution of the acoustic material. In a concert hall, the orchestra is 
surrounded by surfaces that tend to reflect the sound into the audi- 
torium, thereby reinforcing the music in the audience area. The plat- 
form upon which the orchestra is seated usually is of wood. The sur- 
faces surrounding the orchestra are therefore acoustically hard, mak- 
ing the stage relatively live. The audience area, on the other hand, is 
relatively dead. The carpeted floor, wall drapes, upholstered seats, 
and the audience itself, absorb sound. It is therefore reasonable to 
assume that the most natural and satisfactory acoustical conditions 



Sept., 1936] ACOUSTICS IN CONSTRUCTION OF STAGES 



273 



I" OZITE 
*-4" FROM WALL 



ORCHESTRA 
LOCATION 



WELL BRACED WOOD SECTIONS 
OF ORCHESTRA SHELL 



CARPET TO REDUCE 

SOUND REFLECTED FROM 

THE FLOOR INTO THE 

MICROPHONE 



O MICROPHONE 




will be found in scoring stages that are relatively live at the orchestra 
end and relatively dead at the end in which the microphone is placed. 
Experience has indicated that generally the most satisfactory record- 
ing conditions are provided by such an arrangement. 

It is important also to consider a further design feature. The sound 
must be well broken up, or in other words, well diffused, in order to 
provide pleasing re- 
sults. This is par- 
ticularly true in re- 
cording where the 
advantages of bin- 
aural listening can 
not be completely 
utilized. Such dif- 
fusion reduces echoes 
and lessens the 
prominence of first 
reflections which, al- 
though they may not 
be recognizable as 
echoes due to the 
small time delay 
between them and 
the original sound, 
impair recording 
quality. 

A method of ac- 
complishing this dif- 
fusion may be illus- 
trated by referring to 
one of the scoring 
stages recently con- 
structed in Hollywood. Referring to Fig. 2, the design of the 
orchestra shell and the distribution of the acoustic treatment were in 
accordance with the following considerations : 

(1) Parallel hard surfaces were eliminated in order to prevent the reflection 
of sound back and forth between them. 

(2) Large, flat, hard surfaces were not used because of the danger of prominent 
first reflections from such surfaces into the microphone. 

(3) Hard surfaces were not placed at right angles to each other, because 
sound might be reflected from such a combination back to the source. 



FIG. 2. Scoring stage plan. 



274 



D. P. LOYE 



[J. S. M. P. E. 



(4) Convex, rather than concave, curvatures were used in order to avoid sound 
concentrations. Soft absorbing material was placed between adjacent convex 
sections of the orchestra shell. 

(5) The hard orchestra shell surfaces were broken up in an irregular manner 
in order to avoid undesirable acoustic diffraction patterns. 

The reverberation time-frequency characteristic, shown in Fig. 3, 
is smooth, as is desirable. The time at 512 cps. lies within the opti- 
mum band of Fig. 1. The sustained reverberation time at the high 
frequencies makes it possible to attain the brilliance required in 
musical recordings. The increase in reverberation time at the low 



Reverberation time in seconds 

o o p P p . 

fO. M "at P fU 


































































































































































" 






X, 










/* 


- 


^ 










j 




























*^ 




















V 


>d 


\ 
















































































































































































































' J 4 i t ) 




J 




/ 1 3 4 S t 7 t 9 1 t 3 * S t 
100 1000 






KXX> 



Frequency in cycles per second 
FIG. 3. Scoring stage reverberation characteristic. 

frequencies is slight enough to guard against undesirable boominess 
in recordings. 

It has been found desirable, in order to eliminate prominent first 
reflections from the wood floor into the microphone, to place carpets 
or other absorbing materials between the sound-source, such as the 
orchestra, and the microphone. It is obvious that the floor can not 
be broken up, as are the wall and ceiling surfaces, for the purpose of 
reducing the prominence of floor reflections. As an illustration of 
what may happen if such reflections are not avoided, measurements 
were made on a studio stage having a bare floor. The high-speed, 
automatic, level recorder charts of Fig. 4 represent measurements of a 
high-quality reproducing system. The instrument has been pre- 
viously described by Wente, Bedell, and Swartzel. 4 When sound 



Sept., 1936] ACOUSTICS IN CONSTRUCTION OF STAGES 



275 



reaches a microphone by two paths of different lengths, the compo- 
nent sounds alternately reinforce and interfere with each other as the 
pitch of the tone changes. Interference occurs when the wavelength 
of the sound from the loud speakers is twice t.he difference between 
the lengths of the two paths from the speakers to the microphone. 
Interference occurs also for each odd harmonic of this fundamental 
tone. Reinforcement occurs for each even harmonic. In the case of 
the charts of Fig. 4, for instance, the difference between the direct 
path from the loud speakers to the microphone, and the reflected path 
from the loud speakers to the floor to the microphone, was slightly 
greater than 3 feet. This corresponds to a difference in frequency in- 



50 
60 



40 



FREQUENCY 
100 200 500 1000 2000 



20 



3000 4000 5000 6000 7000 6000 



MICROPHONE 6 1 ABOVE FLOOR 




MICROPHONE ON FLOOR 
FIG. 4. Measurements showing effect of prominent floor reflection. 

terval between reinforcements or interferences of 330 cps., which is in 
close agreement with the experimental fact as is evident by inspection 
of the first and second charts of Fig. 4. It can be seen from these 
charts that reinforcement occurred approximately at frequencies of 
300, 600, 900, 1300, 1700, 2000, etc., whereas interference occurred at 
frequencies of 400, 800, 1100, 1500, 1800, etc., cps. 

The first chart was made with the stylus of the high-speed auto- 
matic level recorder moving at the slowest speed of 90 db. per second. 
The second and third charts were made with the stylus moving at 
the rate of 360 db. per second. It is obvious from a comparison of the 
first and second charts that with the stylus moving at the higher 
speed, the acoustic pattern irregularities of the room become evident. 
The second chart, except for such irregularities, is the same as the 



276 D. P. LOYE [J. S. M. P. E. 

first. The third chart was made with the microphone resting upon a 
pad on the floor in order to decrease to a marked degree the difference 
in the lengths of the direct and reflected paths from the speakers to 
the microphone. With the microphone in this position, the difference 
in path lengths was a little less than 2 inches. The calculated differ- 
ence in distance between the paths is in close agreement with the 
results shown by the chart, which indicate that interference occurred 
at a frequency of 4000 cps. and reinforcement at 8000. 

It is evident from this discussion that care should be taken when 
designing scoring stages to reduce the prominence of first reflections 
by breaking up the wall and ceiling surfaces into small irregular areas, 
and by placing absorption upon the floor between the sound sources 
and the microphone. If this is done, greater freedom in the placement 
of the microphone for recording purposes can be permitted. If care is 
not taken, poor quality may result. 

MICROPHONE PLACEMENT 

In recording orchestral music it is desirable, wherever possible, to 
use one microphone rather than two or more connected through a 
mixer to the recording channel. The balance between the various 
instruments of the orchestra with single-microphone pick-up can be 
attained by rearranging the orchestra, bringing closer to the micro- 
phone the instruments that should be made more prominent. This 
applies also when a soloist and chorus are present as well as an orches- 
tra. When the orchestra is used for accompaniment, the soloist is 
usually placed nearest the microphone, the chorus next, and the or- 
chestra somewhat farther back. Acoustic perspective control can be 
achieved to some extent by adjusting the relative distances from the 
microphone of the soloist, chorus, and orchestra. The use of a single 
microphone probably represents the most natural arrangement, the 
microphone taking the place of the listener. Stereophonic or auditory 
perspective recordings are not considered in making this statement. 
Objections, however, have been made to this method of recording 
because of its lack of flexibility and ease of control. When sufficient 
time is not permitted for rehearsals and adjustments, auxiliary con- 
trol methods have been used, which involve the use of more than one 
microphone. Because of the difficulties experienced in obtaining best 
quality under these conditions, preliminary experiments have been 
made to determine the rules under which more than one microphone 



Sept., 1936] ACOUSTICS IN CONSTRUCTION OF STAGES 277 

can be used without noticeably degrading the quality. The results 
attained are described in the following paragraphs. 

When simultaneously using two or more microphones, undesirable 
results similar to those produced by prominent first reflections, de- 
scribed above and illustrated in Fig. 4, may occur unless precautions 
are taken. The automatic level recorder charts of Figs. 5, 6, and 7 
show such effects. Two microphones were placed at different dis- 
tances from a high-quality horn system in the West Coast review 
room of Electrical Research Products, Inc. Their combined output 
was connected through a mixer to the input of the high-speed auto- 
matic level recorder. A warble tone oscillator continuously variable 
from 50 to 8000 cps. was used as the sound-source. In making each 
measurement, the sound volumes picked up by the two microphones 
were adjusted to be equal. Figs. 5 and 6 contain parts of charts, each 
pair representing measurements made, first, with the two microphones 
electrically in phase and, second, with the microphones out of phase. 
The first two charts were made with the microphones each 5 feet from 
the loud speakers. It is evident that with the microphones out of 
phase, the measured sound level was much lower than with the micro- 
phones reinforcing each other. A more exact adjustment of the micro- 
phone positions would have resulted in more complete cancellation, 
and therefore a lower level over the frequency range than shown by 
the second chart of Fig. 5. 

The second and succeeding pairs of charts were made with the dis- 
tances between the microphones increased from 3 inches to 20 feet. 
It will be noted that as the distance was increased, the frequency dif- 
ferences between adjacent reinforcements or interferences was de- 
creased. For example, with the microphones 3 inches apart, inter- 
ferences occurred at frequencies of 2000 and 6000 cps., and reinforce- 
ments at 4000 and 8000 cps. The frequency interval in each case was 
4000 cps. Connecting the microphones out of phase caused the inter- 
ferences to occur where reinforcements occurred with the microphones 
connected in phase. 

Listening tests were made of the quality of sound picked up by the 
two microphones under these test conditions. It was found that 
when the microphones were the same distance from the loud speakers 
and in phase, the quality was pleasing. This might be expected from 
the relatively smooth characteristic curve shown by the first chart of 
Fig. 5. When the microphones were electrically out of phase, the 
sound volume was reduced and the quality impaired. With small 



278 



D. P. LOYE 



[J. S. M. P. E. 











_ i _ /w ^. 














iV\/v' ^ 


"^-v-.-V/^ 








"^""W^W 


i^A^vA^^ 








^- w. 






















































A 






















































































*V J V j\ 


u-V^"^^ 


VUV^ 


VW*^ 


"""^--^ 








v-A - A A/ 


^vw 


^X^^' 


sc 
















wv 








B 





































MICROPHONES TOGETHER - EACH 5' FROM HORNS 



/V * 


-~>- 


~^\/-W 


-"X 
















."^V/V* 






X 


--Y^^VVWV 


Vi ^^Vu-' 


^^v-^^^*^^ 




>""y^ 


^x 


^. , 


















^~X 


sJ 


































A 




































































-^ 


















N^^Vj^^s^ 


f^**^ 


^^^ * 




^_^, 


^~^^ 








AJ ." 


jX-VN/"*-^ 








^^^-^Vuy^ 


V^"" 






Sw ^v 


^\^J~^ 






























B 





































MICROPHONES 3" Af^RT- 5' AND 5-3' FROM HORNS 







^ . 


















-J\sj\r 


r ^ A ^v. / j^ v 


\^~ n ^ T " 


\v v 


\^""^ 


l ^-~**-*% 


s~S^ 


"" ^^^ 


. .^" 












> 


S2 




<v -v^ 




\J 




_5Z 
































A 


















































































^-^J 


*"*~^*^ 






^**V V ^ 




^'--^"^ 




\f 




^j^^r 


















V 












B 





































MICROPHONES 6" APART- 5' AND 5-6' FROM HORNS 













~'"X_ 












^A-AA^- 


^.^/vm^^, 


^"v^ v 


,. -y^'* 


-^N^*-^v--^ ^ 


/ "^^^S-L 


I25s 


/ N^ 


/" 


S3 


\ ^ 








s^ 




^% 






/ 




\f 
































A 




















































































x^vr~" 


^^~~\ 




"v/^^ 


^^v^^ 


^\f^ 


^N / 


\/ 


^\ 


JVX^XN^ 
















V 


V 


































B 
























! 1 






00 200 500 1000 2000 3000 4000 5000 6000 7000 80C 
FREQUENCY M OCLES PER SECOND 



MICROPHONES I' AFttRT - 5' AND 6' FROM HORNS 

FIG. 5. Multiple-microphone pick-up measurements; microphones con- 
nected electrically in phase (^4), out of phase (5). 



microphone separations of 3 inches, for instance, the quality was not 
good, as might also be expected from an inspection of the third and 
fourth charts of Fig. 5. The quality was poorest, in the opinion of the 
listeners, when the microphone separation was 2 feet. At a distance 
of 10 feet, the difference between single-microphone and two-micro- 
phone pick-up was only slight. At a separation of 20 feet, it was diffi- 
cult to notice a difference in quality. 



Sept., 1936] ACOUSTICS IN CONSTRUCTION OF STAGES 



279 



60 


























^Vx\/\/ 


~**^*j\ 


j/***' 


~ r% \ 


f r "^" v f^ ^ 


./Nk ,*-* 


\ r-""v A 


"\ /^~v > 


r \ f/^\ 


/ v 


\f~\f 








^^vv*^ 


V 


^ 




V v 




v 




v ^ 


?o 















































































X"\y"\, 
















WH 


40 


j\s-S~* 







>vAX- 


v " 




'^N/ > 


^v 


/ >> 




gg 
























y 












B 












1 


n 






















3 



60 



20 



60 



20 



MICROPHONES 2' AFftRT - 5' AND T FROM HORNS 



40 
20 
w 






"^ ^y^"' 


\f\s\ 


A A />, , > 


^V\ 


\r\r\i\f 


\f\f\r\ ^ 


SWS 


STO 


W\An 


"w^-v-^yV^j 






w ^/ 


*/ V v v 


J v V 


^ u V v 


* V \/ 






































A 






























i 


















































V'^-^NJ 


f *^\-/ > ^ / 


"\ r>* ''X /A^ 


\^\f^f\ 


AAAA 


AAA/^r 


A \ AA 


r \r\f\/\ 


\A/\/xy\ 


2 20 
_i 




r^2 


JJ_ 




\y \ v v 




/ VV v \ 




J V V 




yvv 
































B 















MICROPHONES 5' APART - 5* AND 10* FROM HORNS 



AA^ 



MICROPHONES K)' AF^RT - 5' AND 15* FROM HORNS 

























* 


..--- 


,^..<J 


v.v- -.- . 


.+ ^':'~S+ 


1 \' '"**'**' j.+ 




^H 


{,/*+<***'* 


Htf*tf**~++ 


^ .. 














' ' 








































A 


















































































sr*f* 


r/^*^_.-''%y. 


^^'* f ''f 


s^-S**''*' 


'"^V^y 




*>x*^ 






_ i v ki2 _ ir 
































B 





































50 KX) 200 500 OOO 20OO 3000 4000 5000 ,6000 7000 8000 

FREQUENCY N OCLES PER SECOD 

MICROPHONES 20" APART- 5' AND 25' FROM HORNS 

FIG. 6. Multiple-microphone pick-up measurements; microphones con- 
nected electrically in phase (4), out of phase (5). 



Fig. 7 represents two supplementary series of tests with the micro- 
phones electrically in phase, the separation between microphones 
being 2 feet in every case. The first, second, and third charts were 
made with the more distant microphone at distances of 7, 15, and 25 
feet, respectively, from the loud speakers. The third chart is a dupli- 
cation of the fourth, except that the stylus of the high-speed level 
recorder was adjusted for maximum speed in the latter case. It is 



280 



D. P. LOYE 



U. S. M. P. E. 











_^ 














rvvvsAA 


w^/Vv 


L TT S*T 


_^u~ 


'" V "X../^ 


\(^~*\f 


X /\ 


r ~\r\ 


/AT" 


N/ "\f 


A/~> 






^"-vy 1 ^ 


_3 


TT 


v v 


/ v 


V . 


/ ' 









































































MICROPHONES 2' APART - 5' AND 7' FROM HORNS 

























/^1 AJl ^ 


LjlAt 


t 




/*~*\ J*^*\ 


y^" v^^ 


<v. y> 


t / 


^ /> 


^A A"\ 


y\ ^. 






\J^^ 


V 


\tT \ 


_ \ 


2_ v 


\ A 


v \ 




^ i i 














^ 








V ' 















































MICROPHONES 2' AF^RT - 13' AND 15 FROM HORNS 




50 00 200 500 1000 2OOO 30OO 4000 50OO 6000 7000 8000 

FREQUENCE IN OCLES PER SECOND 

MICROPHONES 2' AFftRT - 23' AND 25' FROM HORNS 
THE ABOVE CHARTS WERE MADE WITH HORNS DIRECTED TOWARD MICROPHONES 



^j^^^/v^ 




j/\> 




















-j\ff^jj* 


V/v/ 1 ^^ 


vr'^vV^ 


is/V/^A^ jj_ 


"vv'^vvy^is 


L _VV'w/\X 


^' V 


A/V 


AM . ^L. 


















y r Vw^ 


*\/U^ 




\^**fa\. 










































j 


MICROPHONES 2 AFART - 5 AND 7' FROM HORNS 
























-\\v-Al 


. .i 




nVrm_i 


















Ar^yW 


A ^\.V' /-V ' 


^^AA 


M^^vA^A 


*^** f y\ f \sv 


^*V iv'V 


. 




^ 










\r^ 






VWV 


v v^.yy 




^A^ ^. 


k-'-^ v -V^- 















































MICROPHONES 2' APART - 13' AND 15' FROM HORNS 




MICROPHONES 2' APART - 23' AND 25 FROM HORNS 

THE ABOVE CHARTS WERE MADE WITH HORNS DIRECTED AWAY FROM MICROPHONES 
FIG. 7. Measurements showing effect of multiple-microphone pick-up. 



Sept., 1936] ACOUSTICS IN CONSTRUCTION OF STAGES 281 

evident from a comparison of the first three charts that the acoustic 
pattern of the room becomes only slightly more prominent as the 
microphones are moved farther from the speakers. This effect would 
have been more pronounced had not the loud speakers been directed 
toward the microphones. 

In order to accentuate this room effect, the loud speakers in the next 
series of tests, represented by the four charts at the bottom of Fig. 7, 
were rotated 90 degrees, the loud speakers being directed toward one 
side of the room instead of toward the microphones. It is evident 
from the fifth, sixth, and seventh charts that the room-effect over- 
shadowed the interference and reinforcement that occurred when the 
microphones were in the beam of the loud speakers. The reverberant 
energy under these conditions predominated, minimizing the differ- 
ence in quality between single-microphone and multiple-microphone 
pick-up. 

The effect of decreasing the direct energy from the horns as com- 
pared with the reverberant energy, can be seen by comparing the 
fourth chart with the eighth. The level of the sound energy, particu- 
larly at the high frequencies, was reduced by directing the output of 
the speakers away from the microphones. The irregularities through- 
out the frequency range also varied more widely in amplitude under 
the test conditions of the eighth chart of Fig. 7. 

As a result of these preliminary measurements, which should be 
supplemented by further tests under representative recording condi- 
tions, the following conclusions have been drawn : 

(1 ) When two or more microphones are used simultaneously with one recording 
channel, the difference in distance between them and the sound-source should be 
10 feet or greater. 

(2) The sound volume picked up by these microphones should be adjusted to 
differ as widely as is practicable, in order to reduce amplitude variations between 
sound reinforcements and interferences. 

(5) The closer the microphones are to the sound-source, the more important 
it is to observe these rules, because the importance of the direct sound as com- 
pared with the reverberant sound increases as the microphones are moved closer 
to the sound-source. 

(4) The more directional the sound-source, the more important it is to observe 
these rules. In the case of directional musical instruments, the objectionable 
features of multiple-microphone pick-up can be minimized by directing the in- 
struments away from the microphones. 

The author wishes gratefully to acknowledge the assistance given, 
particularly by J. P. Maxfield and E. W. Templin, in collecting the 
data and preparing this paper. 



282 D. P. LOYE [j. S. M. P. E. 

REFERENCES 

1 ST ANTON, G. T., AND ScHMiD, F. C. i "Acoustics of Broadcasting and 
Recording Studios," /. Acoust. Soc. Amer., IV (July, 1932), No. 1, p. 44. 

2 WENTE, E. C.: "Sound Transmission in Rooms," /. Acoust. Soc. Amer., 
VII (Oct., 1935), No. 2, p. 123. 

3 SYMPOSIUM: "Wire Transmission of Symphonic Music and Its Reproduc- 
tion in Auditory Perspective," Electrical Engineering, 53 (Jan., 1934), No. 1. 

FLETCHER H.: "Transmission and Reproduction of Speech and Music in 
Auditory Perspective," /. Soc. Mot. Pict. Eng., XXII (May, 1934), No. 5, p. 314. 

4 WENTE, E. C., BEDELL, E. H., AND SWARTZEL, K. D.: "A High-Speed 
Level Recorder for Acoustic Measurements," /. Acoust. Soc. Amer., VI (Jan., 
1935), No. 3, p. 121. 

DISCUSSION 

MR. WOLF: Those who have had experience in the theaters will recall the days 
when surfaces were treated with metal. We thought then it would be impossible 
to reproduce sound satisfactorily in those theaters, but it has since been found 
that such treatment afforded much low-frequency absorption and provided 
considerable high-frequency brilliance because of the reflections. As a result, 
those theaters were quite satisfactory. The tendency has been, of course, to go 
to lower periods of reverberation at the low frequencies and higher periods at the 
high frequencies. 

There has been recently put upon the market a tile having a diaphragm action. 
If the tile is placed about 1 to 3 inches from the wall, and the sound-wave sets it 
in motion, the sound will be damped by the trapped air. It does not matter 
whether the tile is made of metal or of wood. We have known for a long time 
that if drapes are hung away from the wall they provide considerable low-fre- 
quency absorption. The tile can be damped by simple air damping, or by coating 
its surface with some kind of material. 

MR. KELLOGG: Is it not possible to control the high-frequency and low-fre- 
quency absorptions rather nicely by placing an absorbent material behind a hard 
material having suitably spaced perforations? I can imagine, for example, that 
a hole-spacing can be selected that would afford a reduced absorption above 
5000 cps., by spacing the holes a certain fraction of a wavelength apart. Then, 
if desired, additional absorption at low frequencies might be attained by large 
holes much farther apart, opening into larger cavities. Has that method been 
worked out? 

MR. LOYE: I think the absorption can be more readily controlled by the 
thickness and character of the materials. The spacing of the holes does have a 
bearing upon the absorption characteristic, but I do not believe it is a controlling 
factor unless carried to extremes. 

MR. KELLOGG: I did not fully understand in Fig. 2 whether all the surfaces 
indicated by the zigzag lines were covered with felt, or whether there was a little 
felt only here and there. 

MR. LOYE: The jagged sections forming part of the orchestra shell of Fig. 2 
are made of vertical wood sections, well braced, 20 feet high. Between these 
sections is absorbent material, which is placed several inches away from the 



Sept., 1936] ACOUSTICS IN CONSTRUCTION OF STAGES 283 

hard wall surface of the stage in order to provide the desired low- as well as high- 
frequency absorption. 

MR. KELLOGG: Only a few relatively narrow strips of absorbent? 

MR. LOYE : Yes. All the rest of the material of the orchestra shell is hard. 

MR. TASKER: What is the treatment on the lower walls? 

MR. LOYE : Masonite. This is an actual scoring stage, redesigned from an old 
sound stage to make it suitable for recording music. The reason for breaking it 
up in this manner was to diffuse the sound thoroughly, and allow a wide vari- 
ation in positioning the microphone. 

MR. BAKER: How much selective absorption would result by increasing the 
air-space between the corrugated sections and the wall? 

MR. LOYE: Very little, because the tops of the sections in each case were 
boarded over in order to avoid resonance conditions such as organ pipe effects. 

MR. BAKER: And if the corrugated sections were made of impervious but very 
thin material so that they could respond to the sound vibrations readily ? 

MR. LOYE: Then there would be absorption of a particular kind. We made 
the stipulation that the sections must be well braced and thick enough so as not 
to vibrate in such a manner. We wanted to avoid such possibilities, which might 
have resulted in undesirable resonances. 

MR. KELLOGG: Did you find that placing the microphone against the floor 
was a desirable arrangement? 

MR. LOYE: No, indeed. It was put there only because that was an easy way 
to reduce the difference in distance between the direct and reflected sound paths 
to two inches or less. One can see by the nature of the curve that it would not be 
desirable. 

MR. KELLOGG: The sound-source was some sort of music or speech coming 
from a loud speaker unit? 

MR. LOYE: Yes. 

MR. BAKER: Was the Masonite used on the ends of the wall soft Masonite? 

MR. LOYE : Yes ; and portions of the Masonite were combined with rock-wool 
in order to increase the absorption in that end of the stage. 

MR. BAKER: How were the microphones kept out of phase? Were they really 
out of phase? 

MR. LOYE: Yes. Reversing the connections of one of the microphones will 
put them 180 degrees out of phase. 

MR. KELLOGG: You mean if you had brought them together in position they 
would have been out of phase? Considering the fact they were not adjacent to 
each other there would, of course, be a phase difference in their outputs. 

MR. LOYE: That is right. Considered acoustically, they were not 180 degrees 
out of phase, except in the one case when the microphones were physically placed 
together. 

MR. KELLOGG: Did you put anything behind the wood panels to cause some 
absorption in the trapped air? 

MR. LOYE: Yes; either rock-wool, which was the material on the stage before 
the modifications were made, or soft Masonite. I have forgotten exactly which. 

MR. KELLOGG: Not a masonry wall as shown in the straight-line outline? 

MR. LOYE: No. It is constructed largely of soft Masonite or rock-wool. 



A UNIDIRECTIONAL MICROPHONE* 
H. F. OLSON** 

Summary. Directivity has been found to be desirable in sound -collecting systems 
to improve the ratio of direct to generally reflected sounds and otherwise to discriminate 
against undesirable sounds. The bidirectional ribbon microphone is a pressure- 
gradient instrument, in which the response corresponds to the velocity component in a 
sound-wave. The pressure ribbon microphone is resistance controlled, and the re- 
sponse is a measure of the pressure component in a sound-wave. Combination of the 
outputs of the pressure and velocity ribbon microphones produces a unidirectional 
characteristic. This microphone has been found to be useful in sound motion picture 
recording, radio broadcasting, and sound reinforcing systems in which the desired 
sounds originate in front and the undesired sounds to the rear of the microphone. 

INTRODUCTION 

Directivity has been found to be desirable in sound-collecting 
systems to improve the ratio of direct to generally reflected sound 
and otherwise to discriminate against undesirable sounds. 1 ' 2 One 
of the important factors in a directive sound-collecting system is the 
solid-angle over which sound is received without appreciable at- 
tenuation. This must be sufficiently large to include the area oc- 
cupied by the sources of sound to be received, but at the same time 
the angle must be small enough so that an appreciable gain against 
undesirable sounds is obtained. Another requirement is a direc- 
tional characteristic that is independent of the frequency. A system 
that does not possess this characteristic will introduce frequency 
discrimination. In general, the particular directional characteris- 
tics will depend upon the pick-up problem. For example, the bi- 
directional ribbon microphone has been found to be very useful for 
overcoming excessive reverberation and other undesirable sounds 
and as a tool for attaining a "correct balance" of the received sound. 

The bidirectional ribbon ("velocity" or "pressure gradient") 
microphone 1 ' 3 ' 4 consists of a light, corrugated ribbon suspended in a 
magnetic field. The ribbon is driven from its position of equilibrium 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** RCA Manufacturing Co., Camden, N. J. 
284 



A UNIDIRECTIONAL MICROPHONE 



285 



by the difference in pressure between the two sides. The vibration 
of the ribbon leads to the induction of an emf . corresponding to the 
undulations of the incident sound-wave. The directional char- 
acteristics of this microphone are shown in Fig. 1. 

For certain types of recording it was apparent that a micro- 
phone that had a unidirectional characteristic would be very useful. 
This is particularly desirable in sound motion picture work in which 
the camera may be placed in a region in which the microphone sensi- 
tivity is low and noise from the camera thereby diminished, while 
the actors move about in the high-sensitivity region. Also, in 




Directional characteristic of pressure-gradient microphone : 

E = Eo cos 6. 
FIG. 2. Directional characteristic of pressure microphone: 

E = E . 

FIG. 3. Directional characteristic of combination: E = E (1 + 

cos 0). 

theater sound-reinforcing systems for stage collection the logical 
position of the microphone is in the footlight trough, in which case 
it is desirable to receive sounds emanating from the stage and elimi- 
nate sounds coming from the audience or orchestra. 

The bidirectional ribbon microphone comprises a system in which 
the velocity of the ribbon is in phase with the particle velocity in the 
sound-wave. Referring to Fig. 1, the phase of the output of a 
velocity microphone in the two pick-up zones differs by 180 degrees. 
Now, if this is combined with a microphone in which both the sensi- 
tivity and the phase are independent of the direction (Fig. 2), the 
resulting characteristic will be a cardioid of revolution, as shown 
in Fig. 3, provided that the sensitivity of the non-directional unit is 
equal to the maximal sensitivity of the bidirectional unit. 



286 



H. F. OLSON 



[J. S. M. p. E. 



It is evident that a pressure-operated microphone is required 
that can be incorporated with the bidirectional ribbon microphone 
and at the same time retain uniform response and directional char- 
acteristics. Furthermore, the phase relation between the voltage 
output of the pressure microphone and the pressure in the sound 
field must be suitable for combining with the bidirectional ribbon 
microphone in order to produce a cardioid characteristic. In the 

microphone as finally 
developed, 5 ' 6 Fig. 4, a 
single ribbon is used, 
one part of which is 
velocity operated and 
the other part pressure 
operated. The voltages 
induced in the two por- 
tions are in phase for 
sounds originating in 
front of the microphone 
and are 180 degrees out 
of phase for the opposite 
direction. The direc- 
tional characteristic up 
to a fairly high frequency 
is of the desired cardioid 
shape. It is the purpose 
of this paper to describe 
the theory and operation 
of the combination of a 
pressure and a velocity-actuated ribbon microphone to form a 
microphone having a unidirectional characteristic. 

PRESSURE-ACTUATED RIBBON MICROPHONE 

The pressure ribbon microphone consists of a light metallic ribbon 
suspended in a magnetic field and freely accessible to the atmosphere 
on one side and terminated in a suitable acoustic impedance on the 
other side (Fig. 4). 

The voltage generated by the ribbon is given by the equation 

e = Blx (1) 

where B = flux density 

/ = length of the ribbon 
x velocity of the ribbon 




FIG. 4. Diagram showing essential elements of 
unidirectional ribbon microphone. 



Sept., 1936] A UNIDIRECTIONAL MICROPHONE 



287 

































*~ 











71 


5. 


7 











< 


d 


X 


^ 






























' c 

*s 




. 

1 




ir 







































0* i 


'J 

r 


req 


u 


M 


y 




10' ~ 


I 


J 




6 


1 


a$ 


10* 



FIG. 5. (Upper} Pressure microphone impedance characteristics of com- 
ponents of mechanical system : 

X RP , mechanical reactance of ribbon 
X A p, mechanical reactance due to air 
RAP, mechanical resistance due to air 
RPP, mechanical resistance terminating ribbon 
^, phase-angle between pressure of plane sound- 
wave and ribbon velocity. 

FIG. 6. (Center) Equivalent electrical circuit of pipe damped with tufts 

of felt. 

FIG. 7. (Lower) Theoretical directional characteristics of pressure 
ribbon microphone; assumed to be same as sphere 0.8 inch in diameter. 



288 H. F. OLSON [j. s. M. p. E. 

The ribbon, in a microphone of uniform sensitivity, should have 
at all frequencies the same velocity per unit pressure in the actuating 
sound-wave. Another factor is that of phase: in order to combine 
this microphone with the velocity microphone, the velocity of the 
system must be in phase with the pressure in the sound-wave at all 
frequencies within the transmission band. 

The velocity of the ribbon is given by 

PA* 

(2) 



RPP + RAP + jX RP + JX AP 

where p = pressure in the sound-wave 
AR = area of the ribbon 
The other quantities are as described in the text that follows. 

The mechanical reactance X RP due to the mass of the ribbon 
is shown by the graph of Fig. 5, and is given by the expression 

XRP = jum (3) 

where m = mass of the ribon. 

The mechanical impedance due to the air load upon the ribbon is 

ZAP = RAP -f- JXAP 

The resistive R AP and the reactive X AP components are shown in 
Fig. 5. 

The mechanical impedance due to the electrical circuit and the 
mechanical impedance due to the aperture between the ribbon and the 
pole-pieces are, in general, negligible compared to the other impe- 
dances in the system, and may be neglected. 

An examination of the characteristics X RP , X AP , and R AP shows 
that all increase with frequency. Since, for constant sound pressure, 
the force available for driving the system is independent of the fre- 
quency, the impedance that controls the system should be inde- 
pendent of the frequency in order that the velocity of the ribbon 
should be independent of the frequency. This means that the me- 
chanical resistance R PP terminating the back of the ribbon should 
be larger than the other impedances. Furthermore, the phase- 
angle between the velocity of the ribbon and the actuating force 
should be small. This means that the resistive components should 
be large compared to the reactive components. 

The ideal form of such an acoustic resistance is a long pipe. The 
acoustic resistance of an infinite pipe is 



Sept., 1936] A UNIDIRECTIONAL MICROPHONE 289 



where Ap = area of the pipe. 



TPP = (4) 

A P 



An extremely long pipe is too cumbersome for practical purposes. 
However, it is possible to design a shorter iterative system that will 
be resistive above a certain low frequency. Consider as a specific 
example a pipe 2 meters long, closed at one end, and having a cross- 
section of 1.9 sq. cm., but not loaded with any absorbing material. 
The dissipation in this sort of pipe is small, and the reflection at the 
end will result in standing-wave systems. The particular problem 
here is to introduce sufficient damping so that reflection from the end 
will not occur, and at the same time retain a system that will exhibit 
a pure resistance of constant value over the desired frequency range. 
It has been found that tufts of felt result in very satisfactory damping. 
Fig. 6 shows the method and the equivalent electrical circuit. If the 
quantity of felt is large and packed tightly, M A and r A will be large, 
in which case Z AP will be larger than '42/A P . If the felt is loosely 
packed, M A and r A will be small, and r' A will be large; in this case 
there will be small attenuation in the system and the wave reflected 
from the end will be large, resulting in a non-uniform impedance-fre- 
quency characteristic. By proper choice of the constants, we can ob- 
tain a system that will practically satisfy the conditions of an acoustic 
resistance of the value r AP = 42/A P at the point Z A . Of course, 
obvioUvSly at very low frequencies the system becomes capacitive. 
This is determined by the volume of the pipe. The impedance of the 
pipe was measured on an acoustic impedance bridge and the correct 
proportions of felt determined. 

The mechanical resistance of the pipe referred to the ribbon 
is given by 



(5) 



where A p = area of the pipe 

AR = area of the ribbon 



A true pressure-measuring instrument should not discriminate 
as to direction. To attain this objective in any pressure-measuring 
instrument, the dimensions must be small compared to the wave- 
length of the sound-wave. In the pressure type of ribbon micro- 
phone, where an acoustic resistance line is used in back of the ribbon, 



290 



H. F. OLSON 



[J. S. M. p. E. 



it is difficult to attain absolutely uniform response for all directions 
at the extremely high frequencies because of sound diffraction effects 
around the feed-pipe to the acoustic line (Fig. 4) . The feed-pipe, to- 
gether with the pole-pieces, form a volume around which the sound 
is diffracted. In cases like this it has been found that the diffrac- 
tion around a sphere of equal volume may be computed, and a reason- 
ably good estimate of the performance obtained. 

The volume of the structure involved in this microphone is equiva- 



180 



(50 



240, 



270 




FIG. 8. Directional characteristics of pressure-actu- 
ated portion of unidirectional microphone at various 
frequencies. 



lent to a sphere 0.8 inch in diameter. The theoretical characteris- 
tics for such a sphere are shown in Fig. 7. The observed directional 
characteristics of the pressure component of the unidirectional micro- 
phone are shown in Fig. 8. 

The generated electromotive force developed by the motion of the 
ribbon computed from equations 1 and 2 and the pressure and im- 
pedance values shown in Figs. 5 and 7 is shown in Fig. 9. The experi- 
mentally determined response is also shown in Fig. 9. 



Sept., 1936] 



A UNIDIRECTIONAL MICROPHONE 



291 



-116 
5- -118 

-120 






















1 1 1 1 












x" 
























Fig. 9. 






J 


X 






















( 



















X 
























































o 22 














































8-126 














































6 7 8 9h02 2 3 4 S 6 7 e 

Frequency 


) (0 3 > 3 4 




I0 1 



1 



1.0 10 



O.I 1.0 



0.01 O.I 



^ 




ng. 10. 



/ 



7. 



9, 2 2 3 4 5- 6 76? 3 -? 

Frequency ' u 



15 



10 



~.-Uf> 

,0 -118 
^-120 
S-122 
I-I24 

s 




































































< 



























































^*, 


"X 


> 
























Fig. 11. 














<s 


























































































567 89JQ* 2 : 


4- 5 fc769|Q3 2 345 6789|( 

Frequency 



FIG. 9. (Upper) Theoretically predicted and experimental response 
of pressure-operated ribbon microphone at degree (zero db. - 1 
volt). Note: Data show open-circuit voltage of ribbon. 

FIG. 10. (Center) yelocity microphone; impedance characteristics of 
components of mechanical system : 

XRG, mechanical reactance of ribbon 
XAG, mechanical reactance due to air 
RAG, mechanical resistance due to air 
&p/p, ratio of pressure difference between the 
two sides to the pressure of the sound-wave 
\f/, phase-angle between velocity of ribbon and 

pressure in plane sound-wave. 

FIG. 11. (Lower) Theoretically predicted and experimental response 
of pressure-gradient (velocity) ribbon microphone at degree (zero 
db. = 1 volt). Note: Data show open-circuit voltage of ribbon. 



292 H. F. OLSON [j. s. M. P. E. 

VELOCITY-ACTUATED RIBBON MICROPHONE 

In the velocity ribbon microphone, as previously stated, the ribbon 
is driven from its equilibrium position by the difference in pressure 
between the two sides. This difference in pressure is due to the 
difference in phase between the two sides, and for a plane wave is given 
by the expression, 

Ap = 2Kcp A cos (Kef) sin Kd (6) 

where K = 2ir/\ 

\ wavelength 

p = density of air 

c = velocity 

A = amplitude of <t> 

<f> velocity potential 

d = effective acoustic path between the two sides of the ribbon 

The instantaneous pressure available for driving the acoustical and 
mechanical systems of the microphone is shown in Fig. 10. The 
velocity of the ribbon is given by 



+ RAO 






The mechanical reactance X RG due to the mass of the ribbon is 
shown in Fig. 10, and is given by the expression. The resistive RAP 
and reactive X AP components due to the air load upon the ribbon 
are shown in Fig. 10. The generated electromotive force developed 
by the motion of the ribbon computed from equations 1 and 7 is shown 
in Fig. 11. The experimentally determined response is also shown in 
Fig. 11. 

The foregoing considerations have been concerned with the face of 
the ribbon normal to the line of propagation of the sound. When 
the normal to the face of the microphone is inclined by the angle 6 
to the line of propagation, the air distance from front to back is multi- 
plied by the factor cos 6. 

The observed directional characteristics of the velocity portion of 
the unidirectional microphone are shown in Fig. 12. It will be seen 
that the experimental results are in close agreement with the pre- 
dicted performance. The results indicate that the directional char- 
acteristics of the microphone are practically independent of the 
frequency. 



Sept., 1936] 



A UNIDIRECTIONAL MICROPHONE 



293 



UNIDIRECTIONAL MICROPHONE (COMBINATION OF PRESSURE AND 
VELOCITY MICROPHONES) 



In the preceding sections two types of microphone have been dis- 
cussed: namely, a microphone the response of which is a measure of 
the pressure in a sound-wave, and a microphone the response of which 
is a measure of the particle velocity in a sound-wave. 

The electromotive force generated by the motion of the ribbon due 
to an incident sound-wave in the case of the velocity ribbon micro- 
phone is shown in Fig. 11. Fig. 10 shows that the velocity of the 



180 



240, 




3oo 



330 



FIG. 12. Directional characteristics of velocity- 
actuated portion of unidirectional microphone at various 
frequencies.. 



ribbon, and hence the generated electromotive force, is practically 
in phase with the velocity in a plane sound-wave. 

The electromotive force generated by the motion of the ribbon 
due to an incident sound-wave in the case of the pressure ribbon 
microphone is shown in Fig. 9. Fig. 5 shows that the velocity of the 
ribbon, and hence the generated electromotive force, is practically in 
phase with the pressure in a plane sound-wave. 

Assume that the voltage output e v of the velocity microphone for 
= is made equal to the voltage output e p of the pressure micro- 



294 



H. F. OLSON 



[J. S. M. P.E. 



phone. Now connect the two ribbons in series, and the combined 
output will be 



Cud 



e p -f tv cos 9 



(8) 



The directional characteristic will be as shown in Fig. 3, and is a 
cardioid of revolution with the axis of revolution normal to the 
plane of the ribbon. This combination of pressure and velocity 
ribbon microphone has been termed a uni- 
directional microphone. 

A model of this microphone is shown in 
Figs. 13 and 14. A single ribbon is used, 
divided into two parts, one part of which is 
velocity-operated and the other pressure - 
operated. The velocity portion is left open, 
and the back of the pressure portion is 
terminated in a pipe connected to a labyrinth 
(which is equivalent to a pipe) housed in a 
cylinder as shown in Fig. 14. 

The observed directional characteristics of 
the unidirectional microphone in the horizon - 
tal plane are shown in Fig. 15. It will be 
seen that the observed directional character- 
istics are cardioids of revolution up to fairly 
high frequencies. This substantiates the 
theory of the velocity, pressure, and uni- 
directional microphones. 

The response frequency characteristic of 
the microphone is shown in Fig. 16. It will 
be seen that the response is uniform over a wide frequency range. 
The observed response is in very good agreement with the 
theoretically predicted response. 

The effic iency of energy response of the unidirectional microphone 
as compared to a non-directional microphone for sounds originating 
from random directions, all directions being equally probable, is 




FIG. 13. The unidi- 
rectional microphone. 



Efficiency = 



- 4 7T 



- 



Z*> - 4r 
-0 



Sept., 1936] 



A UNIDIRECTIONAL MICROPHONE 

7T 

(1 + cos 0) 2 sin 6 d6 



2^ / (1 
Jo 



-1 



295 



(9) 



The following conclusion can be drawn : The energy response of the 
unidirectional microphone to sound originating from random direc- 
tions is one-third that of a non-directional microphone. For the same 




FIG. 14. Unassembled view of unidirectional microphone, show- 
ing pressure and velocity portions of the ribbon, magnetic structure, 
labyrinth, and pipe connecting pressure part of ribbon to labyrinth. 

allowable reverberation, the unidirectional microphone can be used 
at 1.7 the distance of a non-directional microphone. 

APPLICATION OF THE UNIDIRECTIONAL MICROPHONE 

The large angle over which this microphone receives sound with- 
out appreciable attenuation indicates that a very wide range of ac- 
tion can be covered with a single microphone. For example, the 
response at 60 degrees is only 2.5 db. below that at degree. On the 
other hand, the response is relatively small for angles larger than 90 
degrees. For example, the response at 120 degrees is 12 db. below 
that at degrees, 17 db. below that at 135 degrees, etc. It has been 
found that this type of directional characteristic is particularly useful 
for creating an illusion of reality, for discriminating against undesir- 
able sounds, for attaining the correct balance of intensities of a group 



296 



H. F. OLSON 



[J. S. M. p. E. 



of sounds, and for controlling the reverberation characteristic of the 
received sounds. 

To enhance the artistic effect of the collected sound it is impor- 
tant that the apparent distance of the sound, as estimated by the 
ear in the reproduction, be compatible with the apparent distance 
of the projected picture, as seen upon the screen. In the case of an 
orchestra, it has been found that the collection distance must be 
relatively large. Equation 9 shows that, with all the other factors 
the same, this distance can be made larger in the case of the uni- 



112 




FIG. 



15. Directional characteristics of unidirectional 
microphone at various frequencies. 



directional microphone. If the non-directional microphone is used 
over the same large distance it is found that the reverberation is, 
in general, very great, and that the reproduced sounds lack definition. 
On the other hand, if the reverberation is reduced by the use of more 
absorption, the brilliance of the recorded sound is reduced because of 
the short period of decay. The use of the unidirectional micro- 
phone makes it possible to achieve (a) more realistic reproduction by 
reason of better definition of the individual instruments, due to the 
greater ratio of direct to reflected sound; and (b) more pleasing re- 
production, by reason of the relatively long reverberation time. 

When one listens normally with both ears he is able to focus his 



Sept., 1936] 



A UNIDIRECTIONAL MICROPHONE 



297 



attention upon the main source of action and subconsciously attenuate 
noises or incidental sounds that may be present. In sound reproduc- 
tion it is important that similar emphasis be placed upon the main 
action and a corresponding discrimination be exercised against 
undesired sounds. Fig. 17 illustrates the use of the unidirectional 
microphone for this purpose. The action centers about the char- 
acters seated at table 2. In the case of a non-directional system, the 
ratio of the direct sounds received from the characters at table 2 to 
that received from the other tables is a function only of the relative 
distances. To attain a satisfactory ratio, in general, means that the 
distance from the desired source to the microphone should be quite 
small. To achieve the correct artistic effect the pick-up distance 
must be comparable to the camera distance. As a consequence, 



CD"' 08 

o-no 

U-II2 
</> 

2-114 
O 


























































- 












i 


>* 


** 


^ 





i 














< 








i 




























































* 120 












































f 6 7 89I0 1 2 3456' 

FRE 


e 9(03 2 3 -4-56769 1( 

:QUENCY 



FIG. 16. Theoretically predicted and experimental response of 
unidirectional microphone at degree (zero db. = 1 volt). Note: 
Data show open-circuit voltage of ribbon. 



when this condition is satisfied the distances from the three tables in 
this example are not widely different. Therefore, by using a direc- 
tional microphone, another parameter is available for attenuating 
the sounds from tables 1 and 3 with respect to table 2. Further- 
more, by properly orienting and locating the microphone the relative 
ratio of the intensities of the sounds from tables 1 and 3 can be ad- 
justed to what one would actually hear were he located at the "dis- 
tance" of the camera. 

Fig. 17 illustrates also the use of the unidirectional microphone 
for reducing noise pick-up from the camera. The camera is located 
behind the microphone ; that is, in the region in which the response is 
small. 

A person listening normally with both ears localizes the azimuth 
of the sound primarily by means of binaural triangulation. In the 
foregoing example an illusion of azimuth is accomplished by adjusting 



298 



H. F. OLSON 



[J. S. M. p. E. 



the relative intensities of the sounds in accordance with what one 
would normally hear in listening to the action first-hand. In listening 
normally the sound is further localized, as regards distance, by the 
time relations between the direct sound and the sound reflected from 
the boundaries, as shown in Fig. 17. If a unidirectional microphone 
is used, the pencils of sound reflected from the walls A and C will be 
attenuated more than those reflected from wall B. The relative time- 
intervals of the direct sound and the sound reflected from wall B 
aid in establishing the perspective of the sound. This illustrates how 




Mlorophon* 



Directional 
Characteristic 




FIG. 17. 



FIG. 18. 



FIG. 17. Arrangement for emphasizing action and discriminating against 
undesired sounds, and for creating illusion of position of source by utilizing 
relative times and intensities of direct and reflected sounds. 

FIG. 18. Arrangement for obtaining correct balance and reverberation of 
instruments of orchestra. 



an illusion of depth or perspective of the recorded sound can be estab- 
lished by the time-interval and the relative intensities of the direct 
and reflected sounds reaching the microphone, and by excluding or 
attenuating sounds that would not normally contribute to the per- 
spective. 

The recording of an orchestra is a salient example of the value of a 
unidirectional microphone. In reproducing music there are two 
important factors: namely, (1) correct balance, or relative intensities 
of the various instruments, and (2) correct reverberation of the re- 
produced sound. In a non-directional system only one parameter, 
the distance, is available for controlling the intensity and effective 



Sept., 1936] 



A UNIDIRECTIONAL MICROPHONE 



299 



reverberation of the recorded sound. However, in the case of the 
unidirectional microphone two parameters are available. A plan 
view of a unidirectional microphone and a group of sound-sources is 
shown in Fig. 18. In this instance sound-source ,$2 is to be em- 
phasized, and is therefore placed upon the axis and quite close to the 
microphone. This results in high recorded intensity and low recorded 



Microphone 



r^' _ 

\ i Souroe* 

i Mil 



BXT*tion 



<r 



Plan 




FIG. 19. (Upper) Arrangement for collecting sounds 
with equal efficiency over an angle of 360 degrees. 

FIG. 20. (Lower) Illustrating the use 'of the unidi- 
rectional microphone for collecting sounds from the stage 
and excluding sounds from the orchestra and audience. 

reverberation. Sound-source S 5 is placed at an angle of 90 degrees, in 
which case an attenuation of the direct sound of 6 db. results, due 
to the directional characteristic of the microphone. This illus- 
trates that practically any value of loudness as well as of effective 
reverberation can be attained by suitably orienting and positioning 
the sound-sources with respect to the microphone. 

In certain types of recording, it is desirable to place the micro- 
phone at the center of the action, directed downward, and collect 
sounds over an angle of 360 degrees with respect to the microphone. 



300 H. F. OLSON [j. s. M. p. E. 

One example of how this may be accomplished is illustrated in 
Fig. 19. Another modification of this arrangement is to place the 
microphone near the floor, pointing upward. 

In public address and sound reenforcing systems the microphones 
are usually placed in the footlight trough or near the front of the 
stage (Fig. 20). Here the directional characteristics of the micro- 
phone are exceptionally suitable because of the desire to pick up 
sounds from the stage and to exclude sounds coming from the or- 
chestra and the audience. 

REFERENCES 

1 OLSON, H. F.: "On the Collection of Sound in Reverberant Rooms, with 
Special Reference to the Application of the Ribbon Microphone," Proc. I. R. .,21 
(May, 1933), No. 5, p. 655. 

2 OLSON, H. F., AND MASSA, F.: "On the Realistic Reproduction of Sound 
with Particular Reference to Sound Motion Pictures," /. Soc. Mot. Pict. Eng., 
XXIII (Aug., 1934), No. 2, p. 63. 

3 OLSON, H. F.: "The Ribbon Microphone," J. Soc. Mot. Pict. Eng., XVI 
(June, 1931), No. 6, p. 695. 

4 OLSON, H. F.: "Mass-Controlled Electrodynamic Microphones; the 
Ribbon Microphone," /. Acous. Soc. Amer., Ill (July, 1931), No. 1, p. 56. 

5 OLSON, H. F. : "A Unidirectional Ribbon Microphone," /. Acous. Soc. Amer., 
IH (Jan., 1932) No. 3, p. 315. 

8 WEINBERGER, J., OLSON, H. F., AND MASSA, F. : "A Unidirectional Ribbon 
Microphone," /. Acous. Soc. Amer., V (Oct., 1933), No. 2, p. 139. 

DISCUSSION 

MR. DEPUE: How does this microphone compare in open space, and in 
response to the wind, with the condenser type of microphone? 

MR. OLSON: It is probably more affected by the wind than the condenser type. 
However, all microphones are affected by the wind, and it is usually necessary to 
use a wind shield. 

MR. KELLOGG: Does the tube that acts as an acoustic impedance shield the 
back over just about half the ribbon height? 

MR. OLSON : It is necessary that the pipe cover a little more than half, in 
order that the output of the pressure ribbon be the same as that of the velocity 
ribbon. 

MR. KELLOGG: Are the pressure and the velocity portions 90 degrees apart 
in phase? Do the two parts of the ribbon act practically independently; or do 
they execute a combined motion due to the combined forces acting on the single 
diaphragm? 

MR. OLSON: The two parts of the ribbon may act independently. For ex- 
ample, for a plane wave striking the microphone from the front, the two ribbons 
vibrate exactly in phase. For the same wave striking the microphone from 
behind, the two ribbons vibrate with a phase difference of 180 degrees. The 



Sept., 1936] A UNIDIRECTIONAL MICROPHONE 301 

ribbon is physically anchored at the boundary between the velocity and the 
pressure sections. 

MR. KELLOGG : Are the pressure and velocity in phase ? 

MR. OLSON: The pressure gradient or resultant driving force is 90 degrees 
ahead of the particle velocity. The mass reactance of the ribbon and associated 
system introduce a lag of 90 degrees. Therefore, the velocity of the ribbon is in 
phase with the particle velocity. 

MR. KELLOGG: the response of the mass being to velocity or pressure gradi- 
ent? 

MR. OLSON: In the case of the microphone, the response corresponds to either 
the pressure gradient or velocity. 

MR. KELLOGG: It has been my understanding of the velocity microphone 
that the diaphragm was so light that it moved practically with the air. 

MR. OLSON: The ribbon is relatively light, and therefore the magnitude of the 
ribbon velocity is practically the same as the particle velocity in the sound-wave. 

MR. KELLOGG: If, by putting some kind of shield behind the velocity micro- 
phone, of highly absorbent material, will a reasonably satisfactory unidirectional 
microphone result? It would not be expected to have the same directional 
characteristic, because its purpose would be to block off completely one-half the 
response; but how good a unidirectional microphone could we make in that way? 

MR. OLSON: If the shield is of dimensions greater than the wavelength, it is 
possible to shut out practically all sound coming from behind. However, a shield 
greater than the wavelength at low frequencies becomes so large that it is imprac- 
ticable. If the shield is smaller than the wavelength, the blocking effect is 
very small. Therefore, a shield of reasonable dimensions would be directional 
for the higher frequencies and non- directional for the lower frequencies. 

MR. WOLF: Does the selective characteristic cause any trouble from certain 
direct reflections? Would a direct reflection from a source stand out more than 
in a non-directional microphone because of the selective characteristic? 

MR. OLSON: Troublesome direct reflections may be eliminated by properly 
orienting the microphone. By employing a directional microphone a direct 
reflection can be made either more outstanding or less outstanding than with a 
non-directional microphone, by changing the azimuth of the microphone with 
reference to the reflected sound. 

MR. WOLF: If the reflections should be more or less discrete, rather than 
occurring as a general reverberation, they might stand out because of that. 

MR. OLSON: That, of course, is possible under certain conditions, but the 
microphone can usually be oriented to reduce or eliminate such reflections. 

MR. WOLF : Are the microphones available at the present time ? 

MR. FRANK: A few have been made for orders, but production lots will be 
available in a few weeks. 



HARMONIC DISTORTION IN VARIABLE-DENSITY 
RECORDS* 



BURTON F. MILLER** 

Summary. Wave-form distortion in variable-density records caused by improper 
track processing and the ribbon velocity effect of the light-valve is considered from both 
theoretical and experimental standpoints. General agreement between calculated and 
experimental values of second-harmonic distortion is attained. Observed values of 
third-harmonic distortion are considerably greater than those predicted by the theory. 
Data obtained indicate that rather high values of distortion may result due to non- 
linearity of the relation between negative track exposure and print transmission. 

Recent advances in the design of theater sound equipment, embrac- 
ing the development of practically flutter-free sound-heads, amplifiers 
of greater power capacity and lower harmonic distortion, and loud 
speaker systems of extended frequency range and higher acoustic 
output ratings have resulted in such an improvement in the fidelity 
of theater reproduction as to warrant increasing attention to the 
degree of distortion present in sound print releases. 

Theoretical and experimental studies of the various elements and 
processes involved in typical motion picture sound recording have 
indicated that the recorder light-modulating device and departures 
from optimal photographic processing of sound-track are responsible 
for a major portion of the distortion normally present in release prints. 
The results of some of these studies pertaining to variable-density 
track as recorded by means of the Western Electric light-valve form 
the basis of this paper. The first portion of the paper will be re- 
stricted to the derivation of equations expressing the transmission of 
the print in terms of the time variations of the geometry of the 
light-valve aperture and the over-all gamma of the print. The 
second portion will be devoted to the presentation of experimental 
data on print distortion, and the correlation of calculated and observed 
values of distortion. 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Warner Bros. Pictures, Inc., Hollywood, Calif. 

302 



Sept., 1936] HARMONIC DISTORTION IN RECORDS 303 

THEORY 

The construction and principle of operation of the Western Elec- 
tric light- valve are now so generally known as to make a detailed de- 
scription of them superfluous. Suffice it to say that the light- valve 
effectively forms a slit whose length remains fixed, and whose width 
is controlled by the magnitude and direction of current flow through 
the ribbon loop that forms the slit. In normal recording practice the 
light-valve slit is illuminated by a light-source of constant intensity, 
and an optically reduced image of the slit is formed in the plane of 
the film in the recording machine. The unmodulated dimensions of 
the slit image are normally of the order of J / 8 inch in length and 
0.0005 inch in width, the length of the slit image being perpendicular 
to the direction of film motion. 

Since the exposure of film is quantitatively measured by the 
product of the exposing light intensity and time of illumination of 
the film, it is apparent that as long as the film passes the slit image 
with constant linear velocity, the negative exposure of any point on 
the film is directly proportional to the time required for that point 
to traverse the width of the slit image. During the process of record- 
ing variable-density sound-track by means of the light-valve, the 
slit-image width varies in direct relation to the variations in wave- 
form of the sound currents passing through the valve ribbons. The 
time of exposure of any point on the negative sound-track is there- 
fore a function of two limits, the first corresponding to the instan- 
taneous ribbon current amplitude at the instant at which the point 
enters the slit image, and the second corresponding to the instan- 
taneous ribbon current amplitude at the instant at which the point 
leaves the slit image. If the slit image were of infinitesimal width, 
the time of exposure of any point on the sound-track would be in- 
finitesimally short, and the exposure of every point on the track would 
be directly proportional to the wave-form of the sound currents 
passing through the light- valve ribbons. Actually, however, the slit 
image is of finite width, and at the higher recording frequencies the 
exposure of the track may depart considerably from the ideal value 
attained with a slit of infinitesimal width. 

The wave-form finally obtained on a variable-density sound print 
is not only dependent upon the wave-form of negative exposure but 
also is a function of the over-all photographic gamma of the print. 
For the case in which the over-all print gamma is unity, and when 
recording is restricted to the straight-line portions of the negative 



304 



B. F. MILLER 



[J. S. M. P. E. 



and positive H&D curves, the print distortion is theoretically equal 
to the wave-form distortion introduced by the light- valve. For cases 
in which the over-all print gamma departs from unity, the print 
distortion is a function of that introduced by the light- valve and the 
processing. 

The wave-form distortion due to the light- valve may be determined 
quite simply by a method similar to that employed by Shea, Herriott, 
and Goehner, 1 which appeared earlier in this JOURNAL. Referring 
to Fig. 1, let MM' and NN' represent the normal unmodulated 



M * 




N 



FIG. 1. 



N' 



Method of determining effect of ribbon velocity 
upon exposure. 



positions of the upper and lower edges of the light- valve slit image, 
respectively. Also, let AB and CD indicate the successive instan- 
taneous positions of the upper and lower edges of the slit image, 
respectively, during sinusoidal modulation of the valve. Let time be 
measured along the neutral axis of the image, OT, and denote the 
average unmodulated width of the slit image by d. Then, for sinu- 
soidal modulation of the slit-image width, the instantaneous upper 
and lower image edge displacements from the neutral axis are given 
by: 



y\ 



d( 

2V 



I -\- m sin co/ 



(D 



Sept., 1936] HARMONIC DISTORTION IN RECORDS 305 

ya = ~ 2 V ~*~ wsina)/ ) ( 2 ) 

where w = 2ir times the applied modulating frequency 
m = modulation fraction. 

For analytical reasons it is advantageous to regard the exposure 
as consisting of two portions; the first portion, 7\, will be regarded 
as that received while the point on the film under consideration 
passes from the upper edge of the slit image to the neutral axis. 
The second portion of the exposure, T z , will be regarded as that 
received while the point on the film passes from the neutral axis to 
the lower edge of the slit image. 

Let the position of any point x on the film referred to the neutral 
axis Or be given by: 

y, = b Vt 

where & is a constant, and 

v is the velocity of the film in inches per second. 

The exposure T\ starts when y s = y iy or when 

b - vh = - 1 1 . + m sin tati j (3) 

and ends when y z = 0, or when 

/, - I (4> 

The value of T\ is therefore given by 



The exposure T% starts when y% = and ends when y 3 = y z , or 

b vt z = "9(1 + m sin w/ 3 J 
The exposure T% is therefore given by 

(6) 



Upon multiplying equations 5 and 6 by to, and rearranging the terms, 
the equations take the form 

/. d \ mud . 

w/1 _ w ^ 2 _ 

and 

w/s ~ 



_ = _. __ sm 



306 B. F. MILLER [j. s. M. P. E. 

The solutions desired are those that express the quantities t\ and / 3 
in terms of the time /2 at which the point on the film under considera- 
tion crosses the axis OT. 

Equations 7 and 8 are of the general form 

x y = a sin x 

Since x and y are odd functions of each other, (x y) may be ex- 
pressed as a Fourier series in y, containing only sine terms. Thus, 
setting 

n = oo 

x - y = ^ sin ny 

n = 1 

where 

C n = - I (x y) sin ny dy 



the coefficients C n take the form 

C n = ? J n (na) (9) 

n 

where the J n (na) are Bessel functions defined by the series 

J.M - gjf [l - ,-effig + 2 . 4(2K ^ +4}.-] < 
The solutions for /i and / 3 thus take the forms 

d \ , 2 M ^ 1 , 



and 



H I 

and the total track exposure, TI + T 2 becomes 



fe - ) (13) 



This result may readily be put into the form 

To = Eo + Ei sin at + 2 cos 2co* + 3 sin 3wt -f ... (14) 



Sept., 1936] HARMONIC DISTORTION IN RECORDS 307 

where 

*-j 

4 _ / wmd\ did 
El = Jl (-*r) COS 2v 

(15) 

2 , /wmd\ . wd 
2 = - / 2 ( - - ) sm - 
co \ v ) v 



etc., 

the solution being valid as long as the maximum rate of change of 
the slit-image width is lower than the velocity of the film. 

From this solution for the sound-track exposure, it is apparent that 
the application of a single frequency to the light- valve results in an 
exposure of complex wave-form, the distortion components that arise 
being functions of the fundamental recorded frequency, the un- 
modulated slit-image width, the percentage of modulation, and the 
uniform film velocity. 

If the over-all gamma of the sound print is equal to unity, the 
print track wave-form is exactly the same as that of the negative ex- 
posure. If, however, the print over-all gamma differs from unity, 
the print track wave-form must be determined from the following 
expression for print transmission : 

T p = K(E + Ei sin ut + 2 cos 2ut + ... ) T <> (16) 

where 

K is a constant 

T is the over-all print gamma. 

Expanding equation 16 as a Taylor's series about the point E , there 
results : 



sin 



T p = E + yoE~ E! sin 



from which the ratio of second harmonic to fundamental is found to 
be approximately given by. 



308 B. F. MILLER [j. s. M. P. E. 

To a similar order of approximation the ratio of third harmonic to the 
fundamental is given by : 



-OS (18) 



When the unmodulated slit-image width is restricted to 0.5 mil, 
and the film velocity to 18 inches per second, as is customary in 
normal recording practice, the argument ud/2v appearing in the co- 
efficients of equation 15 is of such magnitude that the Bessel functions 
may be replaced by the first term of the series 10 defining these func- 
tions. Employing this approximation, the ratio E t /Ei becomes 

. cod 

E 2 = mud * n v 
Ei 4v wd 

COS jr- 

2v 
which becomes further simplified upon setting 

. ud 

sin . 

v ud 



cod 
cos 

2v 



to the value 



By similar substitutions the ratio of Ei/E Q is given to a good order of 
approximation by Ei/E = m. 

Equation 17 may therefore be written in the simple form 



while 18, by similar substitutions, becomes 



these equations being accurate to within 3 per cent for all funda- 
mental frequencies up to about 5000 cps., and for values of 70 lying 
between 0.8 and 1.25. 

Examination of these expressions for H 2 and H s indicates that low- 
frequency distortion is largely caused by departures of the over-all 
print gamma from unity, while at the higher recording frequencies 
the distortion components are largely due to the action of the light- 



Sept., 1936] 



HARMONIC DISTORTION IN RECORDS 



309 



valve. Fig. 2 indicates the theoretical values of print distortion for a 
0.5-mil slit image and for over-all gammas of 0.85, 1.00, and 1.15, 
these curves being based upon equations 19 and 20. 



EXPERIMENTAL DISTORTION DATA 



The theoretical values of distortion as indicated by the curves of 
Fig. 2 attain values considerably in excess of those that would ordi- 
narily be tolerated in any of the amplifier equipment associated with 
either sound recording or reproducing channels. In view of this 



20 



15 



I. Hi - T- 0.85 

1. H 3 - = 

3. H - T" |.00 

5 Hi - T- 1. 13 

6 H, - - - 



MODULATION 



FREQUENCY (C.P.S.) 

400 600 800 1000 




v3000 5000 7000 10,000 



FIG. 2. Theoretical distortion due to effect of ribbon velocity and 
over-all print gamma. 

fact, it becomes a matter of some interest to determine the degree of 
distortion actually found in sound prints recorded and processed 
with typical recording and laboratory equipment. To this end, a 
number of frequency film recordings were made under such condi- 
tions as to render the signal input to the light-valve terminals sub- 
stantially free of all harmonics other than the fundamental. Light- 
valve ribbon spacings of 2.0, 1.0, and 0.5 mil, resulting in unmodu- 
lated slit-image widths of 1.0, 0.5, and 0.25 mil were employed during 
the tests. The exposures were so chosen as to result in unmodulated 
visual diffuse negative track densities of approximately 0.55, the 
development being carried to Eastman time-scale gammas lying 



310 



B. F. MILLER 



[J. S. M. P. E. 



LEGEND : 

1 *- 2 Ml LLIGHT VALVE 

1 MIL. IMAGE 
3 &4- 1 Ml LLIGHT VALVE 

0.5 MIL. I MAGE 
5*6 - 0.5 Mi LLIGHT VALVE 

0.-25MIL, IMAGE 
THEORETICAL 



between 0.36 and 0.39. Sensitometric data obtained during the 
course of development of the test indicated a sufficiently extended 
straight-line portion on the negative H&D characteristics to ac- 
commodate readily the range of density attained in the modulated 
sections of the negative. The positive H&D characteristics, however, 

showed such a limited 
truly straight-line por- 
tion as to indicate the 
necessity of very careful 
choice in unmodulated 
print density if charac- 
teristic curvature distor- 
tion were to be avoided. 

Prints from the nega- 
tives were exposed so as 
to result in visual diffuse 
print densities lying be- 
tween 0.72 and 0.85, 
several different values 
of print control gamma 
being requested. 

The first "take" on 
each negative comprised 
a dynamic over-all 
gamma test, following 
the general method out- 
lined by Albin. 2 This 
test consisted in making 
a series of recordings of 
a constant-level 400- 
cycle tone, approxi- 
mately 25 db. below 
unbiased light-valve 



ZO 



10 




400 



1000 ' 2000 4000 



FIG. 3. Theoretical and observed values of 
second-harmonic distortion due to ribbon- 
velocity effect. 



overload, at a series of valve-ribbon spacings varying from an equiva- 
lent of 20-db. noise reduction to 4-db. noise addition, in seven equal 
logarithmic steps. The over-all projected print gamma was deter- 
mined in each case from calculations based upon the variation in 
reproduced levels from the several steps of the test. Because of the 
apparent accuracy and simplicity of the test, the over-all print 
gammas of each distortion test print were checked by this method. 



Sept., 1936] HARMONIC DISTORTION IN RECORDS 311 

The distortion test portion of each test recording consisted of 20-ft. 
recordings of the following frequencies: 400, 1000, 2000, 3000, 4000, 
5000, 6000, 7000, and 8000 cps. The percentage of track modulation 
was held constant for all frequencies on any one test, but varied from 
test to test between the limits of 25 and 90 per cent. 

Upon receiving the various tests from the laboratory, the prints 
were reproduced through a standard Western Electric sound-head 
and amplifier system, volume indicator readings of the relative levels 
of the several sections of the print being obtained to permit the deter- 
mination of over-all gamma of the print and the frequency response 
characteristic of the complete reproducing system. A band-pass 
filter was inserted into the reproducing amplifier system during the 
observations on the dynamic over-all gamma tests to eliminate errors 
in readings due to film ground-noise components. 

Following these measurements on the prints, 8-ft. loops were made 
of sections of the prints for purposes of distortion analysis. The 
fundamental loop frequencies employed were 400, 1000, 2000, 3000, 
and 4000 cps. The loops were reproduced by the same equipment 
used for determining the print and system frequency characteristics, 
the output of the reproducing amplifier system being suitably attenu- 
ated and applied to the input of a type 636-A General Radio wave 
analyzer. The distortion percentages determined in this manner 
were finally corrected for the relative losses in reproduction of the 
fundamental and the harmonics as determined from the over-all 
print and system characteristic. 

The curves of Fig. 3 indicate the general agreement between the 
theoretical and observed values of distortion for the three values of 
light-valve ribbon spacing employed. Each experimentally deter- 
mined curve represents the averaged data of a minimum of five sets 
of distortion test prints, all data having been corrected for the actual 
over-all print gamma, and expressed in terms of a gamma of unity. 
It will be noted that the observed values of distortion for the case 
of the 0.25-mil slit image depart considerably from the theoretical 
values, the reason for this being yet undetermined. 

Fig. 4 indicates the observed relation between the percentage of 
track modulation and the percentage of second-harmonic distortion 
for the case of a 4000-cycle fundamental. The linearity of the curve 
indicates very good agreement with the theory. 

In general, the values of third-harmonic distortion obtained 
were very much higher than those predicted by the theory. Table I 



312 



B. F. MILLER 



[J. S. M. P. E. 







































/ 


















/* 


















/ 








% ZND HARMONIC 






/ 












/ 


/ 










, 


/ 












\ 


















/ 
























































% MOD. 



















10 HO 30 4-0 -50 60 70 60 90 100 

FIG. 4. Relation between percentage of track 
modulation and observed second -harmonic distor- 
tion for 4000-cycle fundamental (1-mil light-valve). 

indicates the average values obtained for the case of a 0.5-mil slit image . 
under conditions of 80 per cent track modulation and an over-all 
gamma of unity. 

TABLE I 

Average Values of Third-Harmonic Distortion for 0,5-Mil Slit Image 



Fundamental 
Recording 
Frequency 

400 

1000 
2000 
3000 



Theoretical 

Percentage of 

Third Harmonic 

0.029 
0.177 
0.710 
1.200 



Observed 

Percentage of 

Third Harmonic 

1.06 
2.16 
3.06 
3.88 



It is believed that at least a portion of the discrepancy between the 
predicted and the observed results may be charged to directional 
effects in the laboratory developing machines. The sensitometric 
strips attached to each distortion test negative and print indicated 
small, though definite, directional effect characteristics. Because of 
the extreme difficulty of treating the action of this effect upon the 



Sept., 1936] HARMONIC DISTORTION IN RECORDS 313 

developed wave-form, no effort has been made to account for the 
magnitude of the distortion from this source. 

During the course of this distortion study, it was found that many 
of the print dynamic over-all gamma tests exhibited pronounced 
variations in gamma throughout the range of density normally be- 
lieved to lie on the straight-line portion of the positive H&D curve. 
This was particularly true for those prints so exposed as to result in 
unmodulated track densities of approximately 0.70 to 0.75. Dis- 
tortion measurements made on such prints invariably indicated values 
of second- and third-harmonic content that were excessively high, 
Table II indicating a typical set of data from such a print. 



TABLE II 

Variable Gamma Print Distortion, 0.25-Mil Light-Valve Slit Image, 50 Per Cent 

Modulation 

Per Cent Per Cent 

Frequency Second Harmonic Third Harmonic 

400 2.38 1.30 

1000 2.13 1.61 

2000 4.20 1.68 

3000 7.77 2.09 
4000 10.10 



Obviously, it would be an error to include data from such prints 
with those intended to check the distortion introduced by the light- 
valve. Rather, the value of such data lies in the indication that it 
affords of the extremely limited range of unmodulated print density 
that may be employed if print distortion is to be kept at a minimum. 
Still more so, however, such data indicate in a general way a funda- 
mental difficulty present in any system of variable- density sound 
recording, because, regardless of the degree of excellence attained by 
the recording mechanism itself, the fidelity of the final prints obtained 
is limited by the degree of linearity that may be preserved between 
variations in negative exposure and corresponding variations in 
print transmission. It may be argued that push-pull recording would 
limit such distortion to negligible values, and such might be the 
case if it were not for the fact that the third harmonic is likely to be 
quite as objectionable when augmented by push-pull action as the 
second and third harmonics obtained solely from standard track. 



314 B. F. MILLER 

CONCLUSION 

General agreement between the theoretical and experimentally 
determined values of distortion due to the action of the light- valve 
has been attained. From a practical standpoint, it seems likely that 
such distortion is reduced to negligible values when a 0.5-mil ribbon 
spacing is employed in recording. While the curves of Fig. 3 indicate 
appreciable values of high-frequency distortion even in the case of the 
0.5-mil ribbon spacing, it must be remembered that the normal loss 
of efficiency in reproducing the higher frequencies is at present so great 
that the sound energy due to the high-frequency distortion compo- 
nents may be relatively low compared to that of the fundamental fre- 
quencies. It is, in fact, often found desirable to suppress the reproduc- 
tion of any frequencies above 7500 or 8000 cps. by the use of suitable 
low-pass niters, this in itself being some indication of a loss of fidelity 
in recording at the higher frequencies. 

A second factor tending to lessen somewhat the evils of high-fre- 
quency print distortion is found in the nature of the normal spectral 
distribution of energy in speech and music. The probability of the 
occurrence of high-energy-level, high-frequency components in the 
complex wave-forms comprising speech and musical tones is small as 
compared to that existing for the lower-frequency components. 

Distortion arising from non-linearity in the relation between nega- 
tive exposure and print transmission appears to be fully as serious 
at all frequencies within the recording range as the distortion that 
might be attributed solely to the recorder modulating device. This is 
especially true in those cases where release print densities are varied 
from scene to scene for purposes of print volume control. 

Although no data have been presented to indicate the order of mag- 
nitude of distortion components of higher order than the third 
harmonic, measurements on several of the test prints indicated that 
their magnitude was quite negligible. 

REFERENCES 

1 SHEA, T. E., HERRIOTT, W., AND GOEHNER, W. R.: "The Principles of the 
Light-Valve," /. Soc. Mot. Pict. Eng., XVIII (June, 1932), No. 6, p. 697. 

2 ALBIN, F. G.: "A Dynamic Check on the Processing of Film for Sound 
Records," J. Soc. Mot. Pict. Eng., XXV (Aug., 1935), No. 2, p. 161. 



STEREOSCOPY ON THE SCREEN* 
L. LUMlfcRE** 



Summary. Experiments conducted for the purpose of achieving stereoscopic effects 
upon the screen are based upon projecting the stereoscopic pairs to the screen through 
red and green filters such that equal quantities of energy will be transmitted to the 
eyes of the observer, which are fitted with spectacles of the two colors. It is stated 
that this means avoids the eye-strain attendant upon other methods. 



Investigators have long been interested in the idea of obtaining on 
the screen by projection the effect given by the stereoscope. I shall 
not undertake to mention the many solutions that have been sug- 
gested, which, with the exception of Lippman's integral photography 
and Ives' experiments, lead only to a pseudostereoscopic effect be- 
cause they are based upon a single direction of sight. I shall limit 
myself to reminding the reader that Rolhmann and d'Almeida were 
the first to obtain real stereoscopic effects upon the screen. 

In 1855, at a meeting of the Academic des Sciences, d'Almeida 
showed upon the screen images giving the impression of the third 
dimension, produced by superposing upon the screen the two images 
of a stereoscopic pair by means of red and green beams, respectively, 
the spectator being supplied with glasses of the same hues. 

Following these experiments, many endeavored to achieve the same 
effect with beams of colors more or less complementary, sometimes 
yellow and violet, at other times orange and blue. None of these 
solutions, however, corresponded exactly to what is really needed in 
order to avoid eye-strain when looking at these stereoscopic pictures. 

The d'Almeida results remain the most interesting, so far as the 
eye-effect is concerned ; it has been applied in theaters to the pro- 
jection of silhouettes and shadow-pictures giving the sensation of re- 
lief. Frequently, the process has been erroneously referred to as 
"anaglyphs," this word having been coined in 1911 by Ducos du 



* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Paris, France. 



315 



316 



L. LUME&RE 



[J. S. M. P. E. 



Hauron who applied it to a similar but subtractive process, whereas 
the use of colored light proceeds by addition. 

The writer has attacked the problem from a new angle, taking into 
consideration the fact that red and green rays act differently upon the 
eye, especially so far as the persistence of the retina is concerned. 
This difference in reaction was pointed out long ago by Helmholtz for 
rays of wide variation in wavelength. I had occasion to confirm this 
difference for red and green rays in an experiment which I reported in 
a paper to the Academic des Sciences in 1918, and which was the re- 
sult of a chance observation, which was as follows: if, in a photo- 
graphic laboratory lighted by a ruby light, one stands near the safe- 
light lantern and looks at a watch fitted with a phosphorescent dial 
(zinc sulfide plus radium), and then moves the watch slightly but 

quickly, he will be surprised to 
note that the figures seem to 
travel a slight distance over the 
surface of the watch relatively to 
its rim, just as if they were not 
held fast to the face of the 
watch but connected by means 
of flexible links. It results from 
this physiological phenomenon 
that when two images are pro- 
jected upon the same screen, one 
by means of a red beam and the other by means of a green beam, 
it is impossible to obtain a sensation of steady white, and, further- 
more, eye-strain soon becomes unbearable. 

In order to prevent these disturbing effects, I thought that if it were 
possible to receive red and green rays in each eye simultaneously, and 
as it is necessary to blind the left eye to the right image and vice versa, 
the strain would thus be overcome provided the amount of light 
energy received by both eyes were the same. 

To accomplish those two conditions, I used the well known curve 
drawn by Gibson and Tyndall, which shows a maximum toward 5550 
A. For one of the eyes, I chose on the curve, as seen in Fig. 1, a band 
embracing apparently the same amount of red and green, and mea- 
sured with a planimeter what would have to be the boundaries in order 
that the included surface equal half the total surface comprised be- 
tween the whole curve and the axis of abscissas. I came to the con- 
clusion that the transparency of one filter should be limited by the 




500 550 



600 &W 



TOO my 



FIG. 1. 



Gibson and Tyndall response 
curve. 



Sept., 1936] 



STEREOSCOPY ON THE SCREEN 



317 



section lying between 5500 and 6400 A, and that the other filter 
should let pass freely, on the one hand, the portion between 4000 and 
5500 A and, on the other, the portion between 6400 and 7000 A. 

The manufacture of such niters has presented great difficulties as 
regards the choice of the coloring medium ; but the desired result was 






FIG. 2. Arrangement for producing stereoscopic pairs on the film. 

finally achieved and images were projected upon the screen that 
looked like ordinary black-and-white pictures but which could .be 
viewed for several hours without eye-strain. 

The first of the two filters thus obtained is light yellow, and the 
second looks like pure blue. The difficulty in selecting the dyes rested 
on the fact that the dyes had to show the least possible non-selective 
absorption and as sharp as possible limits on the edges of absorption. 




FIG. 3. Arrangement of stereoscopic pairs on the film. 

These conditions were fulfilled by mixing naphthol green, tartrazine, 
and eosine for the first filter; and, for the other filter, by joining a 
blue cyanol tinted glass to another glass tinted with diethylmeta- 
aminophenol sacchareine, it being impossible to mix the latter dyes 
owing to the fact that one is acid and the other basic. 

Having produced good stereoscopic still pictures, I next tried to 
apply the principle to motion pictures. The experimental device 
utilized is shown in Fig. 2. 



318 L. LUMIERE [j. s. M. P. E. 

The two pictures forming the stereoscopic pair are printed upon 
the same film, which runs horizontally so as to produce an image 
practically similar to the one used in monocular vision, losing as little 
as possible of the sensitized surface. 

In this apparatus, reflecting prisms pi and p%, whose principal sec- 
tions are slightly bent toward the horizontal plane passing through 
their centers, reflect the light-beams through the lenses Oi and O 2 . 
The beams then pass through the prisms ps and p, producing the 
images D and G as shown in Fig. 3. 

When projected, the film runs in front of two lenses, whose axes 
are parallel and are cut by a plane parallel to the axis, in order to 
allow homologous centers of the projected images to register in 
height when the distance between the principal axes is made to vary, 
the registering of horizontal parallaxes being effected by moving 
horizontally one of the lenses parallel to its principal axis. In front 
of the two lenses are located the colored filters described above, and 
the spectators are supplied with spectacles of the same hues. 

The stereoscopic effect is then complete, and the spectator is unable 
to estimate his distance from the screen. It seems to him that he is 
in front of an open window, and that the actors are moving within 
the very room. 

The tremendous difficulties involved in the solution of processes 
avoiding the need of placing between the spectator and the screen a 
selecting device, to prevent the two eyes from seeing simultaneously 
the two images of the stereoscopic pair, have led me to the conclusion 
that the process described here, which produces striking effects, will 
lend itself to practical application in theaters in the near future. 

DISCUSSION 

MR. TASKER : A method more or less similar to this, but which does not involve 
an intervening device to give the eye selective vision, has been proposed, but it is 
one that will probably never be developed because of the great likelihood of severe 
eye-strain. The two eyes are separately flooded with light of colors complemen- 
tary to the colors intended to be seen, so that the eyes will, in effect, be blinded 
by the intensity of the light. For example, a strong red light would be projected 
across the theater so it would be seen by the right eye and be outside the line of 
vision of the left; with a strong green light from the other side, seen vividly by 
the right eye and yet out of sight of the left. The ensuing blindness to those re- 
spective colors would permit the alternate images to be seen upon the screen. 
Very probably this can not be done without severe eye-strain. 

MR. RICHARDSON: Has any real progress been made recently in stereoscopy, 
in a way that would permit it to be commercialized in the theater? 



Sept., 1936] STEREOSCOPY ON THE SCREEN 319 

MR. TASKER: The answer to that depends upon personal opinion, as to whether 
or not a method that requires that the spectators wear spectacles of some sort is 
commercially admissible. 

MR. RAYTON: If I understood the paper by M. Lumiere, the point is made that 
the source of eye-strain in viewing pictures projected through two colors, which 
for convenience may be called "anaglyphs," is found in the phenomenon that he 
discovered the apparent shift of figures upon a watch face. That is news to me. 
Whether there is any significance to the observation in this connection, I do not 
know. However, there are certainly other sources of eye-strain involved in pro- 
jection of that kind, and whether the expedient of selecting two filters calculated 
to transmit equal quantities of energy to the eyes of the observer will overcome 
the entire difficulty, I very much doubt. One of the difficulties, of course, is the 
chromatic aberration of the eye because of which the images due to lights of vari- 
ous wavelengths or colors fail to come to the same focus. For example, any 
images of a distant object seen through a blue filter will look out of focus to people 
with normal vision. That has been one of the difficulties in this kind of projec- 
tion, I am sure. My own personal experience confirms the statement. 

Another difficulty in viewing anaglyphs is that of rivalry between the two colors. 
It is my personal experience, for example, that one minute I see the red picture, 
and the next minute the green; then possibly the next instant the two may fuse 
together into reasonable white. What is the cause of that I do not know. Of 
course, it is common knowledge among ophthalmologists that there is such a thing 
as the suppression of one eye or the other in ordinary binocular vision. That 
occurs, they say, rather commonly and frequently. It may be that something of 
that sort is involved. I wish merely to make the point that I can hardly con- 
ceive that the solution proposed will overcome all the difficulties of achieving com- 
fortable vision with stereoscopic projection of this kind. 

MR. RICHARDSON: So far as I am able to observe, the stereoscopic effect seems 
to be enormously exaggerated. 

MR. RAYTON: That is a question of geometry, and probably is deliberate, in 
order to be sure that everybody sees the effect. It is not necessary. If the points 
from which the two pictures are taken are properly chosen, and the distance from 
the observer to the screen is taken into account in designing the projector, perfectly 
normal stereoscopy, or what we might call "orthostereoscopy," can result. The 
same will be true of the polar oid or any other type of stereoscopy. To get a true 
reproduction of three dimensions one must take into consideration the geometry 
of the situation. 

MR. TASKER: A similar comment can be made as to color. When color first 
reached the screen it was very much overdone, in the attempt to make the public 
very definitely color -conscious, as it were. To my mind, the more esthetic efforts 
are those in which the color reaches into the consciousness, so that one realizes 
presently that the scene is more natural than it would have been in black and 
white. In this respect the polaroid method, requiring glasses or the equivalent, 
seems the most promising because it permits the projection of full color as well 
as stereoscopic vision. 

MR. KELLOGG: Mr. Rayton spoke about the suppression of one of the images 
of the red-and-green system. I happen to have had a certain muscular eye 
trouble such that under certain conditions I can not make the two images coincide. 



320 L. LUMI^RE 

When the two images are some distance apart, the suppression of one or the other 
is entirely under my control, and I can switch back and forth from one to the other 
at will. It takes perhaps a second or two to adjust my attention and bring the 
previously suppressed image up to full consciousness. The other image goes out 
at about the same time. 

Another point is of some interest: I have played a little with red-and-green 
stereoscopy, with shadows an old toy. It is quite amusing to reverse the 
glasses. Somebody behind the screen would lift up a small chair and turn it 
around. The chair would seem to be well out in front of the screen, and one would 
feel as if he could unhesitatingly and without error touch any part of it. When 
the chair was rotated, the impression would be that of a perfectly normal chair 
just a black chair, or the silhouette of one. The third dimension was very vivid. 
Now, when the glasses were reversed the chair would immediately become an 
india-rubber chair, tremendously distorted in shape. The near parts would be 
small and the far parts larger. When it was rotated, it would seem to be made of 
rubber, and would undergo weird contortions. If a person would hold out his 
hands near the screen, there would be a vivid impression of his having a tremen- 
dous right hand and a tiny left hand. 

If the stereoscopic or binocular effect is good, the mind automatically places 
more confidence in it than in the perspective. When the two effects work to- 
gether, one has the impression that everything is normal; but when they are 
opposite, he disregards whatever opposing third-dimensional effect he might get 
through perspective, and feels that the object he is looking at is grossly mis- 
shapen. 



THE ELECTRON-IMAGE TUBE, A MEANS FOR MAKING 
INFRARED IMAGES VISIBLE* 



G. A. MORTON** 

Summary. The construction and theory of operation are described of the electron- 
image tube, which consists of a photosensitive cathode, a fluorescent screen, and an 
electron optical system which focuses the electron "image" from the cathode upon the 
viewing screen. Due to the wide spectral response of the cathode, the tube can be used 
to convert infrared, visible, or ultraviolet images into visible images upon the fluorescent 
screen. 

The electron optical system is discussed and its analogy to the conventional optical 
system is shown. To reproduce an image faithfully the electron "lens" system must 
be corrected for various aberrations. Methods of making these corrections are in- 
dicated, and applications of the device are described. 

Considerable interest is attached to the study of images formed by 
radiations in the invisible portions of the spectrum. Images formed 
in these spectral regions can, in general, be made visible by photo- 
graphic methods. The intervention of a photographic process, how- 
ever, necessitates a certain lapse of time between receiving the image 
and viewing it. Often it is desirable to be able to view an image con- 
tinuously while it is being received. 

In the case of an ultraviolet image, continuous observation can be 
accomplished by the use of fluorescent screens. Infrared images can 
not, however, be made visible by this means. To make an infrared 
image continuously visible, it is necessary to resort to electrical meth- 
ods. Certain television systems are capable of rendering continuously 
visible an infrared image, but, however, involve elaborate and com- 
plicated equipment. 

The electron-image tube 1 is a second and much simpler instrument 
for accomplishing the same results. It consists of a photosensitive 
cathode, a fluorescent screen, and an electron optical system to focus 
upon the fluorescent screen the electrons from the cathode. The 
cathode is so sensitized that it will emit electrons when illuminated 



*Presented at the Spring, 1936, Meeting at Chicago, 111. 
**RCA Manufacturing Co., Camden, N. J. 



321 



322 



G. A. MORTON 



[J. S. M. p. E. 



by radiation, which may be ultraviolet, visible, or infrared. If an 
image is projected upon the cathode, electrons will be emitted from 
every point of the cathode surface in proportion to the illumination 
at that region. Close to the cathode the leaving electrons form an 
electrical image which is a reproduction of the light image; they are 
then accelerated to a high velocity and reassembled again into an 
image at the point at which they strike the fluorescent screen. The 
method used to refocus the electrons is one of the most interesting 
aspects of the image-tube and warrants a rather detailed discussion. 
In order to refocus the electrons it is necessary to construct the elec- 
trical equivalent of an opti- 
cal lens. Such an "electron 
lens" is possible because of 
the similarity between elec- 
tron paths through a cylin- 
drically symmetrical elec- 
trostatic field and those 
of light rays through a lens. 



u 




Image Tube 




Optical Analogue 

FIG. 1. Arrangement of elementary elec- 
tron-image tube. 



This similarity is, in fact, 
the basis of the compara- 
tively new science of elec- 
tron optics. 

The basis of the "elec- 
tron lens" in the image- 
tube is the electrostatic 
field formed between two 
coaxial cylinders of equal 
diameters. The arrangement is shown in Fig. 1, as applied to an 
elementary image-tube. This lens is familiar to those who have 
worked in the field of electron optics, and can be shown to have 
properties similar to those of a thick glass lens. It has two separated 
principal planes and two focal points, the positions of these elements 
being dependent upon the velocity of the electrons entering the 
system and the potentials of the two lens elements. The use of 
this lens in the image-tube differs from its usual application in that 
the electrons enter the lens at virtually zero velocity, which fact 
places one of the focal points and one of the principal planes at the 
cathode. This, together with the fact that the index of refraction 
is zero in the cathode region, makes it impossible to apply ordinary 
optics to the system. 



Sept., 1936] 



THE ELECTRON-IMAGE TUBE 



323 



However, it has been possible to calculate the actual potential 
distribution and the electron paths, and from them to determine the 
properties of the lens system. These properties have also been de- 



Focusing Relation 



Magnification 




15 




obv 



FIG. 2. (Left) Relation between cathode-to-lens distance (u) and lens-to- 
image distance ( V) ; (right) relation between these distances and the mag- 
nification. 

termined experimentally by the use of an image-tube with a movable 
cathode and screen. The results of the experimental and theoretical 
investigation are given in Fig. 2. On the left is shown the curve giving 



.03 
O2 


? 


ocuslng Rein 


tion 


y 


.01 


- 




/ 




-JOI 
01 


7" 


/ 






-en 


- j 








'' 


v(Lenu R 


adil) 





15 



1C 



05 



lkvml f teat Ion 



r/ai 



If +>* i- o.f i.o M 

FIG. 3. Relation between ratio of potential of rings and total cathode-to- 
anode potential, and focal length. 

the relation between cathode-to-lens distance, u, and lens-to-image 
distance, V; on the right, the relation between these distances and 
the magnification. It is interesting to note that the magnification 



324 G. A. MORTON [j. s. M. p. E. 

is quite accurately given by V/2u, rather than V/u, as is the case with 
the simple glass lens. 

The image produced by the lens is inverted, as is the image in the 
optical analogue. Furthermore, the lens suffers defects that are very 
similar to those of an uncorrected glass lens. For example, the image 
field is curved in the same sense; the astigmatism of the lens is similar; 
and the image shows marked pin-cushion distortion. Methods of 
correcting these defects will be described later. 




FIG. 4. Showing pin-cushion distortion and blurring, 
before correction. 

The practical difficulty with the system lies in the fact that for a 
given cathode-to-lens distance there is only one position of the screen 
for which the image will be exactly in focus. It is therefore necessary 
to mount the elements extremely accurately or to construct a tube 
in which the elements are movable. Both these solutions involve 
difficult constructions. 

A much more desirable form of lens is one in which the focus can 
be varied electrically. One method of accomplishing this is to make 
the cylinder adjoining the cathode of resistive material, so that a 
potential gradient can be established between the lens and the 



Sept., 1936] 



THE ELECTRON-IMAGE TUBE 



325 



cathode. In actual practice, instead of making the cylinder resistive, 
it is found sufficient to divide it into a number of rings, each of which 
is connected successively to a higher potential. The focal length of 
the system is determined by the ratio of the potential applied to the 
rings and the total potential between the cathode and the anode. 
This relation is shown in Fig. 3. 

The image produced by the system is shown in Fig. 4. The pin- 
cushion distortion and blurring of the image are very evident. With- 
out changing the actual lens system, there are two methods of cor- 
recting these defects. The first is to make the cathode of resistive 

Focusing rings 



Cathode 



Voltage divider 



Screen 



FIG. 5. Image-tube; fixed magnification. 



material, so that a radial potential gradient can be established over 
it; the second is by properly shaping the cathode. 

The first method is not at present of much practical importance, 
although theoretically interesting. The second method, that of 
shaping the cathode, is used in the image-tube with excellent results. 
It has been found experimentally that a cathode curved to a radius 
equal to approximately one lens diameter, combined with the variable- 
focus electron lens system just described, will produce a flat image 
with very little aberration or distortion. This construction is illus- 
trated by Fig. 5. A photograph of the image produced by this 
type of system using the same grid pattern used in Fig. 4 is shown 
in Fig. 6. It will be seen that the image is free from distortion and is 
uniformly sharp. 

The construction of the photosensitive cathode to be used in a given 



326 



G. A. MORTON 



[J. S. M. p. E. 








i 



Sept., 1936] 



THE ELECTRON-IMAGE TUBE 



327 




328 



G. A. MORTON [j. s. M. p. E. 




FIG. 10. Image-tube and microscope, arranged for infrared work. 




FIG. 11. Visable image of micro-specimen illuminated by 
infrared light. 



Sept., 1936] 



THE ELECTRON-IMAGE TUBE 



329 



image-tube will depend upon the spectral region in which maximal 
sensitivity is desired. For the visible and infrared portions of the 
spectrum, a cathode sensitized with cesium on silver oxide is used. 
This surface is similar to that used in a hard cesium photocell, but 
is made very thin, so that photo-electrons will be emitted from the 
face of the cathode when an image is projected upon the opposite 
side. The resolution of this type of image-tube is about 300 lines, 
as can be seen from the resolu- 
tion pattern shown in Fig. 7. 
This limit is not inherent to the 
electron lens, but is due to 
mechanical imperfections of 
cathode and lens. 

In order to illustrate the fidel- 
ity of the image, Figs. 8 and 9 
show photographs of the fluores- 
cent screen when an infrared 
picture is projected upon the 
cathode. 

An interesting use to which 
the image-tube may be put is in 
connection with infrared micro- 
scopy. Fig. 10 shows an image- 
tube and microscope arranged 
for infrared work. The visible 
image of a micro-specimen illumi- 
nated by infrared light is shown 
in Fig. 11. 

Another application is illus- 
trated in Fig. 12, which shows 
an electron telescope in which is 
used an image-tube. With this 




FIG. 12. Electron telescope employing 
the image-tube. 



instrument, it is possible to see objects illuminated by infrared 
radiation. Such a device may be used to test smoke and haze pene- 
tration by infrared rays, for signalling, etc. 

Although at present the sensitivity of the image-tube is such that 
the image is not as bright as the picture projected upon the cathode, 
there is every reason to believe that the sensitivity will eventually be 
increased to a point where the image is brighter than the source, 
a thing impossible in the optics of light. 



330 G. A. MORTON 

REFERENCE 

1 ZWORYKIN, V. K., AND MORTON, G. A.: "Applied Electron Optics," J. Opt. 
Soc. Amer., 26 (April, 1936), No. 4, p. 181. 

DISCUSSION 

MR. KELLOGG: Mr. Morton spoke of the relative brightness of the original 
and the fluorescent screen image. What is meant by the "brightness" of the 
original, when the original is invisible? Also, how much sacrifice of electron emis- 
sion results from the fact that the light reaches the cathode film through the back 
instead of striking the front surface directly? 

MR. MORTON: The term "brightness" is purely descriptive. A better way of 
stating what I mean would be to say that the rate at which the fluorescent screen 
emits radiant energy may be greater than the rate at which radiant energy falls 
upon the cathode. At present, the ratio of the energies is slightly less than unity. 

The absorption of the inert backing of the cathode film is about 50 per cent. 
The photoelectric emission from the type of cathode used in this tube is less than 
one-tenth that of a good photocell. Part of this low sensitivity is due to absorp- 
tion of light going through the film and partly to the nature of the surface itself. 
We have experimental evidence that the photo-emission from the film of photo- 
sensitive material on the cathode may be very greatly increased. 

MR. CRABTREE: How is the brightness contrast varied? What is the limit of 
contrast? Can this be applied to x-ray cinematography ? 

MR. MORTON: The cathode is very insensitive to x-rays. It would be very 
difficult to make an image-tube that could be used in that region of the spectrum . 
I do not know of any material that is a good x-ray photoelectric emitter. Most 
substances can emit x-ray photo-electrons, but very inefficiently. 

The brightness of the image on the fluorescent screen depends upon the photo- 
emission from the cathode, the magnification, and the over-all voltage on the tube. 
At present, 4000 volts are used, but it would be possible to obtain a much brighter 
image if 10,000 volts could be applied. 

MR. TUTTLE: Is there any lag with this particular type of screen? If so, how 
much; and does it increase with the intensity? 

MR. MORTON: The phosphorescent lag in the screen is quite small, of the order 
of V25 second. The phosphorescent decay is more or less logarithmic. 

MEMBER: Is the sensitivity sufficient to use the tube to see, for example, a 
ship entering a harbor in a fog? 

MR. MORTON: The tube will not respond to infrared radiation of wavelengths 
longer than 10,000 or 11,000 A. In order to penetrate fog, infrared radiation of 
wavelengths of 50,000 to 100,000 A must be used. Therefore this form can not 
be used for fog penetration. It can, however, be used to see through haze. 

MR. WOLF: Will Mr. Morton tell us something about the applications of the 
optical system? 

MR. MORTON: At the present time its application is rather limited. It may 
be useful in the field of biology, both as a means of examining organisms that 
would be destroyed by visible light, and of permitting the use of dyes having 
selective absorption in the infrared. In the form of a telescope it can be used for 
signalling, identification, etc. 



NEW MOTION PICTURE APPARATUS 

During the Conventions of the Society, symposiums on new motion picture ap- 
paratus are held, in which various manufacturers of equipment describe and demon- 
strate their new products and developments. Some of this equipment is described 
in the following pages', the remainder will be published in subsequent issues of the 
Journal. 

COPPER-OXIDE RECTIFIERS FOR MOTION PICTURE ARC SUPPLY* 

I. R. SMITH** 



Ten years ago there were perhaps five fairly important types of small rectifiers. 
Each had some degree of merit but all possessed certain positive disadvantages 
that limited their application. Crystal rectifiers, for example, were distinctly 
limited to handling minute amounts of power, such as in radio detection. Wet 
electrolytic rectifiers were messy and required maintenance. Vibrating rectifiers 
got out of adjustment, wore out, were noisy, and caused radio interference. Glass- 
enclosed rectifiers of all types were inefficient at low voltages, uncertain as to 
life. Of the last group, the mercury pool had a satisfactory, long life, but was 
difficult to start, and after it had been started would stop unless a definite mini- 
mum current were kept going. The hot-cathode types did not have the latter 
drawback, but were less satisfactory as to life, particularly for industrial uses. 
Replacements were definitely needed, at best, several times a year. 

With these types in mind, one could have set down readily the requirements 
for the ideal rectifier as one that did not have the various disadvantages of the 
then-existing devices. Such a procedure would have resulted in describing the 
ideal rectifier as one that would be capable of handling any amount of power; 
that would be preferably metallic; dry; quiet in operation; without moving 
parts or contacts; free from radio interference; rugged in form; dependable in 
performance; and economical in operation. 

A real need existed for a rectifier with such characteristics. This need became 
most pressing during the days of direct-current radio because of A -battery charg- 
ing requirements, and by a fortunate turn of events it was just at that time that 
the copper-oxide rectifier was ready for the market. The first units made were 
A -battery trickle chargers, just 10 years ago. In this field the rectifier found ready 
acceptance, and literally millions were sold, because it was generally recognized 
that here was a rectifier that appeared to approach the ideal already described. 
It was metallic, had no moving parts, was noiseless in operation, set up no radio 



* Presented at the Spring, 1936, meeting at Chicago, 111. 
** Westinghouse Electric & Mfg. Co., East Pittsburgh, Pa. 



331 



332 



NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 




FIG. 1. Voltage-current relation 
for typical 1.5-inch diameter disk. 



interference, was rugged in form and 
gave promise of long life in operation. 
The need for such a rectifier proved to 
be so real that it practically supplanted 
other types in the radio battery charg- 
ing field. 

It was recognized at the time, of 
course, that the radio activity was 
likely to be short-lived, so that if the 
rectifier were to continue in existence 
its use would have to be extended into 
other fields. Intensive study of the 
rectifier characteristics was then under- 
taken so that we might know exactly 
to what extent the rectifier could be 
applied industrially. A thorough in- 
vestigation was made of the voltage- 
current relations in the two directions 
of conduction, the effect upon these 
of different temperatures, the limita- 
tions as to current-density and voltage 
gradients, the changes in character- 
istics as the result of operation and 
age, as well as many lesser points. 
The study of the rectifier, its proper- 
ties, and the process of making it is 
still going on. 

The application of the rectifier to 
industrial uses, then, has been going 




-4-3-1-10 1 3 4 

FIG. 2. Voltage-resistance relation for typical 
1.5-inch diameter disk. 



Sept., 1936] 



NEW MOTION PICTURE APPARATUS 



333 



o.i- 



\ 



\ 



\ 



\ 



100 



on for many years, and has proceeded to an extent greater than perhaps is 
generally realized, until today the copper-oxide rectifier has been accepted as 
standard equipment in many applications in which reliability and sturdiness 
are paramount. 

RECTIFIER CHARACTERISTICS 

Basically, a copper-oxide rectifier is about as simple a piece of equipment as 
can be imagined. An elementary rectifier in the most usual form consists of a 
washer of copper, one side 
of which is covered com- 
pletely with red or cuprous 
oxide. Such a washer, pro- 
vided it has been properly 
made, has the remarkable 
characteristics shown in 
Fig. 1. Here are shown the 
voltage-current relations in 
the two directions of con- 
duction of a typical P/Vhich 
diameter disk. In the low- 
resistance or forward direc- 
tion, with 3 volts, for 
example, impressed across 
the disk, a current of 9 
amperes will flow. When 
the voltage is reversed, the 
current drops to 1 milli- 
ampere, so that the ratio of 
resistance in the two direc- 
tions is 9000 to 1. The same 
data are plotted in Fig. 2 in 
terms of voltage and re- 
sistance. 

These resistance values are 
not constants, but are found 
to vary considerably with 
the temperature of the 
washer, and, to some extent, 
with age. It is important to 

note that as the temperature changes, the resistance varies, not in the direc- 
tion one might expect in a device that is about 95 per cent copper, but in the 
opposite direction. In other words, as the temperature rises, the resistance de- 
creases. The general nature of these changes is shown in Fig. 3, which contains 
typical resistance curves over a temperature range of 40 to +60C., for a 
constant impressed voltage. 

Certain changes in these characteristics were found to occur with time, both in 
the forward and backward directions. In the forward direction the resistance 
tends to increase as time goes on, the amount of increase depending upon the 



FIG. 3. Resistance- temperature curves for 
typical 1.5-inch diameter disk, measured at 
1.25 volts d-c. 



334 



NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 




FIG. 4. Exaggerated view of single disk unit 
construction. 




FIG. 5. Typical Rectox units. 



Sept., 1936] 



NEW MOTION PICTURE APPARATUS 



335 





















x 


x 


















^x 


X 




















X 


^ 










90 1 








/ 


x 















c 






/ 


















I 

t 




/ 


/ 






















/ 




















X 


X 

















































i 











; 




j 


X) 











FIG. 6. Effect of increase in area of radiating 
fins on ability of stack to dissipate heat, showing 
watts dissipated by 8-inch stacks for 20C. tem- 
perature rise; fins spaced best distance apart. 



temperature at which the rec- 
tifier is maintained; the 
higher the temperature, the 
greater the change. In the 
back direction substantially 
no change takes place except 
while the unit is in opera- 
tion, during which time the 
back resistance decreases. 

The characteristics of the 
washer having thus been de- 
termined, the next step is to 
build the complete rectifier 
stack. The method of as- 
sembly has proved to be 
rather important. While the 
copper-copper-oxide washer 
is a rectifier complete in 
itself, it was necessary to 
devise means of getting the 
current into and out of it. The outside oxide surface has considerable contact 
resistance, so if a terminal is simply laid upon it the resistance between it and 
the oxide will be so great that the rectifier will not be able to function properly. 
So the contact resistance had to be reduced by graphiting the surface with 
rubbed-in carbon. Furthermore, it was found that the oxide surface was 

actually not smooth, but was 
all hills and valleys, so that 
a hard, flat terminal would 
contact only part of it. This 
led to the use of a soft lead 
washer next to the oxide, 
forced by pressure into inti- 
mate contact with the entire 
surface of the oxide. Then it 
was possible to complete the 
assembly with any suitable 
terminal, or with more disks 
or radiating fins, as might be 
desired. The general con- 
struction is illustrated in 
Fig. 4. 

With such an assembly, it 
was possible to build up 
satisfactory units similar to 
those shown in Fig. 5, but 
before the units could be 
FIG. 7. Variation in total loss at different tern- applied, methods had to be 
peratures. found for determining what 




336 



NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 




FIG. 8. Comparison of total loss curve at 
different temperatures with temperature rises of 
different types of units at various values of watts 
dissipated: (.4) unit with no radiating fins; (B) 
unit with 3-inch diameter fins; (C) unit with 
4-inch diameter fins, fins spaced best distance 
apart; (D) total loss. 



electrical ratings could be 
obtained from them. 

BASIS OF RATINGS 

Ratings are based pri- 
marily upon the fact that 
the copper-oxide rectifier is a 
resistance device. Washers 
will divide the load in 
parallel, then, inversely as 
their forward resistance, and 
in series will divide the 
voltage directly as the re- 
sistance. So it could be 
said, to begin, that if reason- 
able care were taken to pre- 
vent large differences in 
washer resistances, washers 
could be connected in series 
or parallel to any extent 
desired. If this had not been 
possible, obviously the appli- 
cation of the rectifier would 
have been greatly restricted. 

Since the rectifier is a 
resistance device, it is evi- 
dent that when current flows 



through it in the forward direction, or voltage is applied that sends leakage current 
through in the back direction, there will be PR losses that will generate heat in 
the rectifier. The effect of heat upon the characteristic has already been dis- 




FIG. 9. Single motion picture arc rectifier stack. 



Sept., 1936] 



NEW MOTION PICTURE APPARATUS 



337 



cussed, as illustrated in Fig. 3. A study of this characteristic shows that as 
temperature increases the tendency is for leakage current to increase faster, 
and evidently if the rise in temperature is not halted, the current in the high-re- 
sistance direction may reach dangerous proportions, approaching a short circuit. 
So the matter of dissipating the heat generated and keeping the rectifier tempera- 
ture down to a safe value had to be given close attention. 

The dissipation of heat losses is, of course, something with which every engineer 
is constantly concerned. The method adopted here was that of cooling by con- 
vection. By using properly sized and spaced radiating fins, it was possible to dissi- 




FIG. 10. 



Arrangement of 12 stacks for 65-ampere, 33- 
volt output. 



pate the heat and keep the temperature of the units down to a safe point. Fig. 6 
compares the performances of radiating fins of various sizes, all spaced the best 
distance apart, showing how many watts can be dissipated by stacks of disks 
8 inches long, the temperature rise in each case being 20C. For example, if no 
fins are used, a dissipation of 10 watts will result in the 20 rise. If 2V4-inch diam- 
eter fins are used, the dissipation can be increased to 12 watts; with 3-inch fins 
to 16 watts; and with 4-inch fins to 31 watts. Thus, by the addition of radiating 
fins the watts dissipated per stack have been increased three times for the same 
temperature rise. Since the watts to be dissipated depend directly upon the volt- 
age and current per disk, it follows that the use of fins permits a very considerable 
increase in the disk rating. 



338 



NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 



This in itself, however, was not sufficient to establish the correct rating. It was 
necessary to determine also what combination of voltage and current could be 
used. A given unit operating, for example, with an output of 3 volts and 6 amperes 
might have substantially the same. loss and temperature rise as with an output of 
6 volts and 3 amperes; but that alone would not be a sufficient criterion of the 
correctness of the rating. The final analysis had to take into account the safety of 
the rating, which depends upon how the losses vary with temperature. That is, 
the total losses had to be calculated at various operating temperatures, so that 
their trend would become evident, and this had to be compared to the heat- 
dissipating ability of the 
type of unit structure being 
considered. An example will 
help to make this clear. 

Let it be assumed that it is 
desired to make a bridge 
type full-wave unit having 
one disk in each leg, and 
having a d-c. output of 4.5 
volts, 0.5 ampere. The first 
step would be to calculate 
the back losses in the unit 
operating at this output. 
This is done over a range 
of operating temperature 
from 20 to 80C. f and the 
result is the curve of Fig. 7. 



20 



Temperature (C)- 
I I I 

60 80 



FIG. 11. Comparison of watts loss at differ- 
ent temperatures in motion picture rectifier unit 
with temperature rise curve of the same unit at 
different watts dissipation. 



This procedure is then re- 
peated for the forward losses, 
as shown also in Fig. 7. 
These show the opposite 
tendency, as is to be ex- 
pected. The next step then 
is to add the two loss curves, 
resulting in the total loss 
curve of Fig. 7. A minimum point is found at 60 C., which, of course, is the 
point of maximum efficiency since the same output is assumed throughout. 

The final step is to select the unit structure that will be capable of taking care 
of the losses. This is accomplished as shown in Fig. 8. Three curves are plotted, 
all originating at 25 C., which is taken as the ambient temperature. These 
curves are for units with 04) no radiating fins, (B) with 3-inch fins, and (C) 
with 4-inch fins, each at the best spacing, and show what temperature rise will 
result in any of these types of structure for various watts per disk dissipated 
within the unit. 

In Fig. 8 is plotted also the total loss curve (D) of Fig. 7. The conclusions to 
be drawn are obvious. Curve A shows no intention of coming anywhere near 
curve D; hence a unit with no radiating fins could not be worked at this rating. 
Curve B is approximately tangent to curve D. However, a slight rise in ambient 
temperature, for example, would result in the two curves failing to touch. Curve C 



Sept., 1936] 



NEW MOTION PICTURE APPARATUS 



339 



crosses curve D almost at right angles, and evidently the ambient temperature 
could rise considerably and the curves would still intersect. 

The 4-inch fin construction then would be selected as suitable for handling 
such a rating. The unit would operate at the point at which the curves crossed, 




FIG. 12. 



Complete motion picture arc rectifier for 65- 
ampere, 33-volt output. 



or a rise of 20 C. above ambient. The unit would be quite stable, that is, would 
have no tendency to run away because of a slight increase of temperature, from 
whatever cause. Needless to say, the loss calculations must be based upon the 
unit characteristics after aging, not when new. 

By the same method then, any unit rating can be examined and its correctness 
checked so that all guesswork is eliminated. 



340 NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 

FAN COOLING 

It will no doubt be apparent from this discussion that any method of lowering 
the unit temperature will permit an increase in unit rating. For a given flow of 
air past the unit, as with natural draft, this was accomplished by increasing the 
size of the radiating fins. Likewise, for a given size of radiating fin, the same result 
can be attained by increasing the flow of air. Thus, if forced draft is used, tem- 
perature will be lowered and ratings may be increased. As it is possible to increase 
the flow of air enormously with a quite inexpensive fan, the size and cost of the 
rectifier for fairly large outputs can be reduced to a surprising extent from what 
would be needed with natural draft. 

The unit design that would be best for fan cooling must derive the maximum 
benefit from the air passing the unit, must result in uniform distribution of the air 
so that all the units will be cooled equally and no hot-spots developed, and must 
proportion the unit ratings to the fan capacity so that the whole will be properly 
balanced. Careful laboratory study over a long period of time of different types 
of construction, sizes, and spacing of radiating fins at different measured volumes 
of air flow, resulted in the type of unit shown in Fig. 9. These units are mounted 
side by side and close together in a symmetrical arrangement, as shown in 
Fig. 10, and when mounted in an air duct in proper relation to a suitable fan, 
constitute a fan-cooled rectifier. 

The correct rating is again determined, as before, by comparing the losses at 
the rated output with the temperature rise curve of the units under forced draft. 
The result of this analysis is shown in Fig. 11 for the design used for operating 
motion picture arcs. The desired output is, for example, 65 amperes at 33 volts. 
This, reduced to a watt-per-disk basis, results in losses at various temperatures 
as shown in curve B. The unit shown in Fig. 9, with an air-flow of 60 cubic feet 
per minute, can dissipate losses with temperature rise as in curve A. The two 
curves cross nearly at right angles. It may be noted that the losses continue to 
decrease even up to 80C., so that the design is quite stable. 

A complete motion picture rectifier, then, consists of an assembly of units simi- 
lar to Fig. 10, mounted so that the units are ventilated by suction from a fan, 
and the necessary transformers, relays, and terminal boards, all enclosed in a sheet- 
steel ventilated cabinet. Fig. 12 shows a typical completed assembly. Trans- 
formers are generally furnished with primary line voltage taps and secondary taps 
for close adjustment of the output voltage. Relays are included for protection 
of the rectifier unit to prevent operating unless the fan is energized. The entire 
unit weighs only 250 pounds and is 31 inches high, 20 inches wide, and 17 inches 
deep. 

Usually one unit or its equivalent is needed for each arc. Since nearly always 
two arcs are to be operated, some economy results by mounting two sets of units 
in the same case, using the same transformer and fan, one set being connected to 
each arc. Care has to be taken with such a design to assure proper ventilation for 
all the units. 

LIFE TESTS 

When the rectifier was first put into commercial form, life tests were commenced 
so that we might know as quickly as possible what limitations existed in this 
direction. Now there are operating on test hundreds of units of various types 



Sept., 1936] NEW MOTION PICTURE APPARATUS 341 

from 1 to 10 years old, all of which have given the same answer, namely, that the 
life of the rectifier when properly applied is indefinite. The performance with 
time of a Rectox used to operate a printing telegraph will serve as an example. 
In 3 years of continuous operation at full load, the output has dropped off only 
7 per cent. Tests made on a standard 3-phase, elevator-controlled Rectox, so 
far covering 27,600 hours of operation, show similar results. The rectifier was 
connected directly to the a-c. line without intervening resistance, and no adjust- 
ment of voltage or load is ever made. In a 7 1 / 2 -year test, or 65,000 hours, a num- 
ber of 2-ampere, 6-volt battery chargers are still delivering rated output, with no 
indication of any limit to the life of the rectifier. 

The use of Rectox rectifiers for operating motion picture arcs, then, is not a 
radically new departure, but merely another step in a process that has been going 
on for years, the application of the rectifier to industry. As in the past, each new 
application is carefully studied, and once all the facts are known, the rectifier has 
never failed to function as expected. Its usefulness as a tool in many other fields 
has long been known. Now we believe the same experience will be had in the 
motion picture field. In fact, it appears that rectification by copper-oxide has 
already been accepted by the industry as a highly satisfactory method of supply- 
ing the projection arc. 

REFERENCES 

ELDERKIN, J. K.: "Theoretical and Practical Aspects of the Copper-Oxide 
Rectifier," Internal. Projectionist, 9 (Dec., 1935), No. 6, p. 18. 

GRONDAHL, L. O.: "The Copper-Cuprous Oxide Rectifier and Photoelectric 
Cell," Rev. Modern Phys., 5 (April, 1933), No. 2, p. 141. 



APPLICATION OF THE COPPER-OXIDE RECTIFIER TO MOTION 
PICTURE PROJECTION* 



C. E. HAMANN** 



The application of the copper-oxide rectifier as a d-c. power supply for pro- 
jection is by no means new. A fan-cooled type of copper-oxide rectifier was de- 
veloped by the General Electric Co. in 1930, and applied successfully to the 
low-intensity type of lamp as well as the Hi-lo lamp. 1 With the advent of the 
Suprex type of arc an entirely new field has been opened up. The characteristics 
of the copper-oxide rectifier have been found to be admirably well adapted to the 
special voltage and current requirements of the Suprex arc and in this service 
it is rapidly supplanting other types of equipment. 

Construction. General constructional details of a typical commercial unit 
are illustrated in Fig. 1. The transformers and control panel are assembled as a 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** General Electric Company, Bridgeport, Connecticut. 



342 



NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 



unit and located in the upper part of the casing. The copper-oxide stacks, 
together with the air baffles and the blower system, are also assembled as a single 
unit and installed in the lower part of the casing. Aside from these two unit 
assemblies, the only other parts are the control relays and protective switch. 

Circuit Design. It has been previously pointed out that single-phase rectifica- 
tion is not suitable for the Suprex arc due to the pronounced ripple in the d-c. 




FIG. 1. Interior view of copper-oxide rectifier for pro- 
jection service. 

voltage output. 2 Hence, copper-oxide rectifiers for Suprex supply have been de- 
veloped for polyphase service only. The rectifier circuit is designed for full- 
wave rectification of all three phases of the a-c. supply, and the resulting d-c. 
output has a ripple of relatively low magnitude and high frequency (360 peaks 
per second for 60-cycle, 3-phase). 

The only noticeable effect of the d-c. ripple is a slight "sing" to the arc, which, 
it has been determined experimentally, can be eliminated by a small reactance 



Sept., 1936] 



NEW MOTION PICTURE APPARATUS 



343 



filter in the d-c. circuit. However, visual inspection supplemented by photo- 
metric tests indicate that the ripple is not of sufficient magnitude to cause any 
discernible effect in the light upon the screen. Therefore, the additional cost of a 
filter reactance does not appear warranted, and is omitted in the commercial de- 
sign. 

A typical circuit diagram of a 3-phase unit is illustrated in Fig. 2. The trans- 
former connections are arranged delta-delta. Units for 2-phase service differ 
only in transformer design. A Scott-connected transformer changes 2-phase to 
3-phase, so that the rectifier circuit and the output characteristics are identical 
to those of the 3-phase unit and therefore need not be discussed separately. 



Transformers 




D-c circuifc 
}Arc 

}HOV.a-c. 
Three-phase, 

FIG. 2. Standard arrangement of internal wiring of 3-phase 
G. E. copper-oxide rectifier. 



An examination of the wiring diagram will readily disclose the general scheme 
of the rectifier circuit, but a brief explanation of the control circuit may be in 
order. It will be noted that the blower motor and the relay holding coils are 
energized from a separate 110- volt single-phase circuit. The purpose is two- 
fold: (a) it provides a simple remote-control arrangement for starting and 
stopping the rectifiers; and (b) it permits operating the rectifier on two phases in 
the event of failure of any one of the phases of the 3-phase a-c. supply line. 

Design Data. In the design of a copper-oxide rectifier it is customary to base 
all calculations upon established data for the "unit bridge." 1 For a single-phase 
circuit a "unit bridge" consists of four disks or elements arranged in a full-wave 



344 



NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 



"bridge" circuit as shown in Fig. 3a. For a 3-phase circuit, with which this paper 
is chiefly concerned, the "unit bridge" consists of 6 disks arranged in a 3-phase 
full-wave "bridge" as shown in Fig. 3b. 

Experience over many years has resulted in establishing certain standard 
limits of voltage, current, and temperature for the unit bridge. Thus, dividing 
the safe voltage limit of the unit bridge into the desired voltage rating indicates 
the number of disks that must be connected in series in each leg of the bridge cir- 
cuit. Similarly, the current limit of the unit bridge divided into the desired 
current rating indicates the number of parallel groups of disks required in each leg 
of the bridge circuit. 

The problem of design would be simple except that consideration must be 
given to the so-called "aging" characteristic of the copper-oxide element. 1 This 
can be denned as a gradual increase of resistance of the unit in the "forward" 
direction which tends to stabilize after 4000 to 5000 hours of use. 



A-C, 



Dj 
CE 




3-Phace Supply 
123 






(a) (b) 

FIG. 6 (a) Arrangement of single-phase "unit bridge" circuit; (b) 
arrangement of 3-phase "unit bridge" circuit. 



Aging is a function of temperature as well as of time, and the higher the operat- 
ing temperature the greater will be the change of resistance before stabilization 
takes place. It is at once apparent that in order to maintain the initial output of a 
unit it will be necessary to increase somewhat the applied a-c. voltage after aging 
has taken place. 

Care must be taken in the design to make sure that the final applied a-c. 
voltage necessary to maintain the rated output after aging will not exceed a safe 
value for the particular disk combination under consideration. Fortunately, 
sufficient data have been collected over a period of years to predict with reason- 
able accuracy the amount of aging that will take place for any given conditions of 
temperature. 

In the commercial design, illustrated in Figs. 1 and 2, eight taps are provided 
on each transformer secondary winding, making it possible to adjust the applied 
a-c. voltage in steps of approximately 2 volts. This serves the dual purpose of 



Sept., 1936] 



NEW MOTION PICTURE APPARATUS 



345 



permitting a wide range of output adjustment and a ready means to compensate 
for aging. 

In Fig. 4 is shown a family of curves giving the d-c. volt-ampere output regula- 
tion for each of the eight secondary taps on a standard 65-ampere unit. These 
curves illustrate the inherent regulation of this type of rectifier that makes it 
possible to operate without any form of external ballast in the arc circuit. It 
will be seen that the entire range of output, from 40 to 65 amperes, 30 to 35 volts, 
can be covered with the five lower taps, leaving three additional taps to compensate 
for aging, an amount that experience shows is more than ample. 

Operating Efficiency. The efficiency of a copper-oxide rectifier is regarded as 
the ratio of the d-c. watts' output to the a-c. watts' input. The losses in the rectifier 
consist of resistance losses in the forward direction through the copper-oxide ele- 
ments, leakage in the "blocking" direction, and transformer losses. In the case 




10 30 40 50 60 70 



FIG. 4. Volt-ampere output characteristics 
of standard 65-ampere G. E. copper-oxide 
rectifier. 



of the fan-cooled motion picture rectifier, the power consumed by the fan motor 
and the control relays should be added to the input to obtain the true over-all 
efficiency. Resistance losses in the copper-oxide elements represent the major part 
of the total losses. It has been previously shown that this resistance tends to 
increase with age up to a certain stabilizing point. It is at once obvious that 
aging tends to reduce somewhat the initial efficiency. 

There is no rule-of-thumb method of stating the new and aged efficiencies of 
any rectifier, because the difference depends upon the ratio that the rectifier 
resistance bears to the total impedance of the rectifier-load circuit. If the rectifier 
resistance is a small part of the total impedance of the circuit, then a considerable 
change in rectifier resistance will mean only a slight change in the total impedance 
of the circuit, and consequently only a slight change in efficiency. 

Aging being a function of temperature, an adequate system of forced ventila- 
tion will permit operating at a considerably higher current-density per unit 



346 



NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 



bridge than would be the case with the conventional air-cooled type of unit. 
Tests on fan-cooled units operating at various current densities continuously since 
1929 have given the necessary data for establishing safe limits with respect to cur- 
rent density and temperature. 

With a fan-cooling system capable of limiting the temperature rise of the copper- 
oxide elements to a maximum of 2 or 3 degrees C., a maximum current density of 
2 amperes per unit bridge (3-phase) appears safe. It may be concluded that 
under these conditions it will not be necessary to apply an a-c. voltage in excess 
of 8 volts per unit bridge in order to maintain an output of 7 volts d-c. per unit 
bridge after aging has taken place. 



80 
70 

60 
50 

80 
90 

60 






























o" 










Jig. 5, 
















































































































































































D-C. 1 Ampere* 










40 50 60 71 










D- 





Amperei 


I 











*. 

I 

<H" 

O 




































ng. 6, 






































= 


= 


" 


"'i 1 ' 







- 1 !- 







__ 





i 



i^r^ 
*. 




i 





















































































FIG. 5. Efficiency (new) of standard 65- 
ampere G. E. copper-oxide rectifier. 

FIG. 6. Upper and lower limits of pre- 
dicted efficiency of standard 65-ampere G. E. 
copper-oxide rectifier. 



Fig. 5 shows the over-all operating efficiency of a standard 65-ampere unit 
(new), and includes the power consumed by the fan motor, relays, and protective 
switch. Fig. 6 shows the upper and lower limits of the predicted efficiency after 
aging has taken place. 

It should be kept in mind that several thousands of hours of continuous use are 
required before the aging begins to approach stabilization, and this, measured in 
terms of theater service, is a matter of years. 

Inspection of Fig. 5 indicates a somewhat higher efficiency at 40 amperes than 
at the full-load point of 65 amperes. By increasing the number of parallel groups, 



Sept., 1936] NEW MOTION PICTURE APPARATUS 347 

and in this way reducing the current-density per unit bridge, it would be possible 
to make the point of maximum efficiency coincide with the full-load point on the 
curve, but the increase in size and cost of the unit would more than offset any 
possible advantage from the slight gain in efficiency. 

On the other hand, any attempt by the designer to economize on materials by 
reducing the number of parallel groups and increasing the current-density per unit 
bridge will mean increasing the impressed voltage to a point in excess of the 
maximum safe limit of 8 volts per unit bridge, thus introducing a risk of possible 
breakdown by puncturing the oxide film. 

Life. It has been frequently stated that a copper-oxide rectifier properly 
applied will last indefinitely. Factory life-tests now running into the tenth year 
as well as hundreds of different industrial applications all tend to bear out this 
claim. 

The percentage of troubles in the field has been gratifyingly small, and such 
troubles as have occurred are usually traceable either to misunderstanding the 
operation of the unit or to overloading due to inadequate wiring and equipment. 

Conclusion. There are at the present time upward of 600 G. E. motion picture 
type copper-oxide rectifiers in the field, which furnishes ample proof of the ac- 
ceptance of this type of equipment by the industry. Good engineering and strict 
adherence to the design limits described above should result in a high degree of 
reliability, exceptionally long life, and freedom from trouble. 

Aging, if given proper consideration when designing the rectifier, will result 
in only a small reduction in operating efficiency over a period of years. A careful 
check of a number of units in service for more than a year indicates that they are 
still maintaining their original output with no change in adjustment. 

The Projection Practice Committee of the Society 2 early recognized the merits 
and advantages of the copper-oxide rectifier, and others who unhesitatingly pre- 
dicted its success in the motion picture field are seeing their predictions well on 
the way toward fulfillment. 3 ' 4 ' 5 ' 6 

REFERENCES 

1 HARTY, E. A., AND HAMANN, C. E.: "Fundamental Characteristics and 
Applications of the Copper-Oxide Rectifier," General Elect. Rev., 36 (Aug., 1933), 
No. 8, p. 342. 

2 Report of the Projection Practice Committee, /. Soc. Mot. Pict. Eng., XXIV 
(Jan., 1935), No. 1, p. 35. 

3 "Copper-Oxide Rectifier for Projection Arc Supply," Internal. Projectionist, 8 
(March, 1935), No. 3, p. 15. 

4 RUBIN, H. : "Power Sources for the Suprex Arc and Operating Costs," Better 
Theatres (June 29, 1935), p. 20; Ibid. (July 27, 1935), p. 20. 

5 RICHARDSON, F. H.: "Bluebook of Projection," Quigley Publications, New 
York, N. Y. (1935). 

6 CAMERON, J. R.: "Servicing Sound Equipment," Cameron Pub. Co., Wood- 
mont, Conn. 



COMMITTEES 

of the 
SOCIETY OF MOTION PICTURE ENGINEERS 

(Correct to August 20, 1936; additional appointments may be made at any time 
during the year as necessity or expediency may require) 



L. W. DAVEE 
A. S. DICKINSON 



ADMISSIONS 

T. E. SHEA, Chairman 
M. W. PALMER 
H. RUBIN 



H. GRIFFIN 

D. E. HYNDMAN 



O. M. GLUNT 
A. C. HARDY 



BOARD OF EDITORS 
J. I. CRABTREE, Chairman 



L. A. JONES 

G. E. MATTHEWS 



W. H. CARSON 
O. O. CECCARINI 



COLOR 

J. A. BALL, Chairman 
C. H. DUNNING 
R. M. EVANS 

A. M. GUNDELFINGER 



H. W. MOYSE 

A. WARMISHAM 



H. GRIFFIN 



H. BUSCH 

A. S. DICKINSON 

G. C. EDWARDS 



CONVENTION 
W. C. KUNZMANN, Chairman 

J. H. KURLANDER 

EXCHANGE PRACTICE 
T. FAULKNER, Chairman 

A. HlATT 

J. S. MACLEOD 



M. W. PALMER 



N. F. OAKLEY 
H. RUBIN 
J. H. SPRAY 



T. ARMAT 

G. A CHAMBERS 



A. N. GOLDSMITH 
A. C. HARDY 



HISTORICAL 

E. THEISEN, Chairman 
W. CLARK 



HONORARY MEMBERSHIP 
J. G. FRAYNE, Chairman 



G. E. MATTHEWS 
T. RAMSAYE 



H. G. TASKER 
W. E. THEISEN 



348 



COMMITTEES of THE SOCIETY 



34<) 



E HUSE 

K. F. MORGAN 



JOURNAL AWARD 
A' C. HARDY, Chairman 



G. F. RACKETT 

E. A. WlLLIFORD 



J. CRABTREE 
R. M. EVANS 
E. HUSE 
T. M. INGMAN 



LABORATORY PRACTICE 

D. E. HYNDMAN, Chairman 
M. S. LESHING 
C. L. LOOTENS 
R. F. MITCHELL 



H. W. MOYSE 

J. M. NlCKOLAUS 

W. A. SCHMIDT 
J. H. SPRAY 



MEMBERSHIP AND SUBSCRIPTION 

E. R. GEIB, Chairman 



Atlanta 

C. D. PORTER 

Boston 

T. C. BARROWS 
J. R. CAMERON 
J. S. CIFRE 

Camden & Philadelphia 
H. BLUMBERG 
J. FRANK, JR. 

Chicago 
B. W. DEPUE 
J. H. GOLDBERG 
S. A. LUKES 
R. F. MITCHELL 



Cleveland 
R. E. FARNHAM 
J. T. FLANNAGAN 
V. A. WELMAN 

Hollywood 
J. O. AALBERG 
L. E. CLARK 
G. H. GIBSON 
C. W. HANDLEY 

E. HUSE 

F. E. JAMES 

G. A. MITCHELL 
P. MOLE 

K. F. MORGAN 
G. F. RACKETT 

Minneapolis 
C. L. GREENE 



New York 

G. C. EDWARDS 

J. J. FINN 

G. P. FOUTE 

H. GRIFFIN 

W. W. HENNESSEY 

R. C. HOLSLAG 

M. D. O'BRIEN 

F. H. RICHARDSON 

H. B. SANTEE 

T. E. SHEA 

J. L. SPENCE 

J. H. SPRAY 

Rochester 

E. K. CARVER 

Washington 
N. GLASSER 

F. J. STORTY 



Australia 
H. C. PARISH 

Austria 

P. R. VON SCHROTT 

China 

R. E. O'BOLGER 



Canada 

F. C. BADGLEY 

C. A. DENTELBECK 

G. E. PATTON 



England 

W. F. GARLING 

R. G. LlNDERMAN 
D. McM ASTER 

R. TERRANEAU 
S. S. A. WATKINS 



350 



COMMITTEES OF THE SOCIETY 



[J. S. M. P. E. 



France 

L. J. DIDIEE 

L. G. EGROT 

F. H. HOTCHKISS 

J. MARETTE 

Germany 

W. F. BIELICKE 

K. NORDEN 

Hawaii 

L. LACHAPELLE 



T. ARMAT 

H. T. COWLING 



O. B. DEPUE 



D. P. BEAN 
F. E. CARLSON 
W. B COOK 
H. A. DEVRY 



India 

H. S. MEHTA 
L. L. MISTRY 
M. B. PATEL 

Japan 

T. NAGASE 

Y. OSAWA 

New Zealand 
C. BANKS 



Russia 

A. F. CHORINE 

E. G. JACHONTOW 

Travelling 

E. AUGER 

K. BRENKERT 

W. C. KUNZMANN 

D. McRAE 

O. F. NEU 

H. H. STRONG 



MUSEUM 

(Eastern) 

M. E. GILLETTE, Chairman 

G. E. MATTHEWS T. RAMSAYE 

E. I. SPONABLE 
(Western) 
E. THEISEN, Chairman 

J. A. DUBRAY A. REEVES 



NON-THEATRICAL EQUIPMENT 

R. F. MITCHELL, Chairman 
E. C. FRITTS 
H. GRIFFIN 
R. C. HOLSLAG 



J. H. KURLANDER 

E. Ross 
A. SHAPIRO 
A. F. VICTOR 



C. N. BATSEL 
L. N. BUSCH 
A. A. COOK 
L. J. J. DIDIEE 



J. I. CRABTREE 
A. S. DICKINSON 



PAPERS 
G. E. MATTHEWS, Chairman 

M. E. GILLETTE H. B. SANTEE 

R. F. MITCHELL T. E. SHEA 

W. A. MUELLER P. R. VON SCHROTT 



L D. WRATTEN 



PRESERVATION OF FILM 
J. G. BRADLEY, Chairman 
R. EVANS 
C. L. GREGORY 
T. RAMSAYE 



V. B. SEASE 
W. A. SCHMIDT 



M. ABRIBAT 
L. N. BUSCH 
A. A. COOK 
R. M. CORBIN 
J. A. DUBRAY 



PROGRESS 

J. G. FRAYNE, Chairman 
R. E. FARNHAM 
E. R. GEIB 
G. E. MATTHEWS 
H. MEYER 
V. E. MILLER 



R. F. MITCHELL 
G. F. RACKETT 
P. R. VON SCHROTT 
S. S. A. WATKINS 
I. D. WRATTEN 



Sept., 1936] 



COMMITTEES OF THE SOCIETY 



351 



M. C. BATSEL 
J. I. CRABTREE 



J. O. BAKER 
T. C. BARROWS 

F. E. CAHILL 
J. R. CAMERON 

G. C. EDWARDS 
J. K. ELDERKIN 



PROGRESS AWARD 

A. N. GOLDSMITH, Chairman 



PROJECTION PRACTICE 
H. RUBIN, Chairman 
J. J. FINN 
E. R. GEIB 
A. N. GOLDSMITH 
H. GRIFFIN 
J. J. HOPKINS 
C. F. HORSTMAN 
P. A. McGuiRE 



C. DREHER 
J. G. FRAYNE 



R. MIEHLING 

E. R. MORIN 

M. D. O'BRIEN 

F. H. RICHARDSON 
J. S. WARD 

V. WELMAN 



PROJECTION SCREEN BRIGHTNESS 



A. A. COOK 
A. C. DOWNES 
D. E. HYNDMAN 



C. TUTTLE, Chairman 
W. F. LITTLE 
O. E. MILLER 
G. F. RACKETT 
H. RUBIN 



B. SCHLANGER 

A. T. WILLIAMS 
S. K. WOLF 



J. R. CAMERON 
J. J. FINN 



M. C. BATSEL 
L. E. CLARK 
F. J. GRIGNON 



F. C. BADGLEY 
M. C. BATSEL 
L. N. BUSCH 
W. H. CARSON 
A. CHORINE 
A. COTTET 
L. DE FEO 
A. C. DOWNES 
J. A. DUBRAY 
P. H. EVANS 



W. C. KUNZMANN 
J. H. KURLANDER 



PUBLICITY 

W. WHITMORE, Chairman 
G. E. MATTHEWS 

SOUND 

P. H. EVANS, Chairman 
K. F. MORGAN 
O. SANDVIK 
E. I. SPONABLE 

STANDARDS 

E. K. CARVER, Chairman 
R. E. FARNHAM 
C. L. FARRAND 
H. GRIFFIN 
R. C. HUBBARD 
E. HUSE 
C. L. LOOTENS 
W. A. MACNAIR 
K. F. MORGAN 
T. NAGASE 

STUDIO LIGHTING 
R. E. FARNHAM, Chairman 
V. E. MILLER 
G. F. RACKETT 



P. A. McGuiRE 
F. H. RICHARDSON 



R. O. STROCK 
H. G. TASKER 
S. K. WOLF 



N. F. OAKLEY 
G. F. RACKETT 
W. B. RAYTON 
C. N. REIFSTECK 
H. RUBIN 

0. SANDVIK 
H. B. SANTEE 
J. L. SPENCE 
A. G. WISE 

1. D. WRATTEN 



E. C. RICHARDSON 

F. WALLER 



352 COMMITTEES OF THE SOCIETY 

SECTIONS OF THE SOCIETY 

(Atlantic Coast) 

L. W. DAVEE, Chairman 
H. G. TASKER, Past- Chair man M. C. BATSEL, Manager 

D. E. HYNDMAN, Sec.-Treas. H. GRIFFIN, Manager 

(Mid-West) 

C. H. STONE, Chairman 

R. F. MITCHELL, Past-Chairman O. B. DEPUE, Manager 

S. A. LUKES, Sec.-Treas. B. E. STECHBART, Manager 

(Pacific Coast) 

G. F. RACKETT, Chairman 

E. HUSB, Past-Chairman K. F. MORGAN, Manager 
H. W. MOYSE, Sec.-Treas. C. W. HANDLEY, Manager 



FALL, 1936, CONVENTION 



ROCHESTER, NEW YORK 

SAGAMORE HOTEL 
OCTOBER 12-15, INCLUSIVE 



Officers and Committees in Charge 

PROGRAM AND FACILITIES 

W. C. KUNZMANN, Convention Vice-P resident 
J. I. CRABTREE, Editorial Vice-P resident 
G. E. MATTHEWS, Chairman, Papers Committee 
H. GRIFFIN, Chairman, Projection Committee 
E. R. GEIB, Chairman, Membership Committee 
W. WHITMORE, Chairman, Publicity Committee 
G. E. MATTHEWS, Chairman, Papers Committee 



G. A. BLAIR 

A. A. COOK 

J. I. CRABTREE 

K. M. CUNNINGHAM 



LOCAL ARRANGEMENTS 
E. P. CURTIS, Chairman 
K. C. D. HICKMAN 
L. A. JONES 
G. E. MATTHEWS 



I. L. NIXON 
W. B. RAYTON 
E. C. ROLAND 
L. M. TOWNSEND 



E. R. GEIB 



F. E. ALTMAN 
E. K. CARVER 



J. G. CAPSTAFF 
E. K. CARVER 



A. A. COOK 
W. H. REPP 



REGISTRATION AND INFORMATION 
W. C. KUNZMANN, Chairman 

S. HARRIS 
TRANSPORTATION 
C. M. TUTTLE, Chairman 

J. G. JONES J. C. KURZ 

H. B. TUTTLE 

HOTEL ACCOMMODATIONS 

K. M. CUNNINGHAM, Chairman 

A. A. COOK O. SANDVIK 

H. B. TUTTLE 

PROJECTION 
H. GRIFFIN, Chairman 

E. C. ROLAND E. F. TETZLAFF 

L. M. TOWNSEND 



353 



354 FALL CONVENTION [j. s. M. p. E. 

BANQUET 

I. L. NIXON, Chairman 

G. A. BLAIR R. M. EVANS S. E. SHEPPARD 

W. CLARK W. C. KUNZMANN H. B. TUTTLE 

A. A. COOK J. S. WATSON 

PUBLICITY 

W. WHITMORE, Chairman 

F. C. ELLIS J. C. KURZ G. E. MATTHEWS 

E. C. FRITTS E. C. ROLAND 

LADIES' RECEPTION COMMITTEE 

MRS. L. A. JONES, Hostess 

assisted by 

MRS. A. A. COOK MRS. C. M. TUTTLE MRS. H. B. TUTTLE 

MRS. R. M. EVANS MRS. S. E. SHEPPARD 

TECHNICAL SESSIONS 

All technical sessions will be held at the Sagamore Hotel (Convention head- 
quarters) except the session on Tuesday morning, which will be held in the audi- 
torium of the Kodak Research Laboratories at Kodak Park. 

HEADQUARTERS 

The Headquarters of the Convention will be the Sagamore Hotel, where 
excellent accommodations are assured. A reception suite will be provided for 
the Ladies' Committee, which is now engaged in preparing an excellent program 
of entertainment for the ladies attending the Convention. 

Special hotel rates guaranteed to SMPE delegates, European plan, will 
be as follows: 

One person, room and bath $ 3.50 

Two persons, room and bath 6.00 

Parlor suite and bath, for two 10.00 

Parlor suite and bath, for three 12.00 

Room reservation cards will be mailed to the membership of the Society in 
the near future and everyone who plans to attend the Convention should return 
his card to the Hotel promptly in order to be assured of satisfactory accommo- 
dations. Registrations will be made in the order in which the cards are received. 
When the Sagamore Hotel is booked to capacity, additional accommodations will 
be provided by the Hotel Arrangements Committee at another hotel in the 
immediate vicinity of the Sagamore. 

A special rate of fifty cents a day has been arranged for SMPE delegates 
who motor to the Convention, at the Ramp Garage, near the Hotel. 

Golfing privileges may be arranged for any of the Convention delegates by 
consulting the Chairman of the Local Arrangements Committee. 

REGISTRATIONS 

Registration Headquarters will be located on the Sagamore Roof. All mem- 
bers and guests are expected to register, as admittance to certain sessions may be 
contingent upon the display of a membership badge or special ticket. Admit- 



Sept., 1936] FALL CONVENTION 355 

tance cards will be issued at the registration desk for the special lecture on Mon- 
day evening and for the invitation luncheons on Tuesday and Wednesday noons 
at Kodak Park and the Bausch & Lomb Optical Company, respectively. Reser- 
vations for the Informal Luncheon on Monday and for the banquet on Wednes- 
day should be made at the registration desk. 

Identification cards will be honored at Loew's Rochester and the Century and 
Palace Theaters, the latter two through the courtesy of the Monroe Amusement 
Company. 

SEMI-ANNUAL BANQUET 

The Semi-Annual Banquet and Dance of the Society will be held at the Oak 
Hill Country Club on Wednesday, October 14th, at 7:30 P.M., at which time the 
Progress and Journal Awards will be made. Motor-coach transportation will be 
provided to and from the Club by the Transportation Committee. 

ROCHESTER RESTAURANTS 

In addition to the Main Dining Room and the Coffee Shop at the Sagamore 
Hotel, where excellent meals may be obtained, there are several leading restau- 
rants in the downtown district, as follows: 

Laube's Old Spain, 11 East Avenue 

Odenbach's Restaurant, 14 South Avenue 

Odenbach's Coffee Shop, Clinton and Main (Dinner Dancing) 

1078 University Ave. A reasonably priced family restaurant. 

Manhattan Restaurant, 25 East Avenue 

Seneca Hotel, 26 Clinton Avenue S. 

INVITATION LUNCHEONS AND INSPECTION TRIPS 

The Eastman Kodak Company has invited all visiting members of the Society 
to a complimentary luncheon at Kodak Park on Tuesday, October 13th at 1:10 
P.M. Inspection trips through the Kodak Park Works and the Kodak Research 
Laboratories will be arranged during the afternoon. 

On Wednesday, the Bausch & Lomb Optical Company has invited all visiting 
members to a complimentary luncheon at their plant on St. Paul Street at 1:10 
P.M. An inspection tour of the plant and the Scientific Bureau will be arranged 
following the luncheon. A special trip through the B & L glass plant will start 
at 8:30 A.M. (at the plant) Wednesday morning. 

The details of several other trips, for which reservations should be made, are as 
follows: 

Stromberg Carlson Telephone Manufacturing Co., 100 Carlson Road. Two- 
hour trip, including engineering and acoustical research laboratories and manu- 
facture and assembly of radio sets and telephone equipment. 

Delco Appliance Corporation, 391 Lyell Ave. Two-hour trip Tuesday and 
Wednesday afternoons. Trip includes examination of finished product display, 
visit to engineering laboratories, and tour of the plant departments housing 
interesting product operations. Registration for visit desired. 



356 



FALL CONVENTION 



[J . S. M. P. E. 



Gleason Works, 1000 University Avenue. One-hour trip showing manufacture 
and assembly of gear machinery. Advance registration desired. 

Taylor Instrument Co., 95 Ames St. Two-hour trip showing manufacture of 
clinical and household thermometers, aneroid barometers, industrial tempera- 
ture recorders and controllers, etc. Engineering and Research Laboratories 
and special display of instruments in operation. Advance registration desired. 

Wards Natural Science Establishment, 302 N. Goodman St. This firm specializes 
in supplying models for museums, schools, and colleges. Trips may be arranged 
at any time without previous registration. 

It is assumed that delegates will arrange for their own transportation for all 
industrial trips with the exception of those to the Bausch & Lomb Optical Co. 
and the Kodak Park Works of the Eastman Kodak Co., for which motor-coach 
service will be provided on the dates specified. 



9:00 a. m. 



10:00 a. m.-12:00 m. 



PROGRAM 
Monday, October 12th 

Sagamore Hotel Roof 
Registration 
Society business 

Committee reports 
Technical papers program 



12:30 p.m. 



Sagamore Hotel Main Dining Room 

Informal Get-Together Luncheon for members, their 
families, and guests. Brief addresses by several 
prominent members of the industry. 



2:00 p. m.-5:00 p. m. 



Sagamore Hotel Roof 

Technical papers program. 



8:00 p. m. 



Eastman Theater 

"Color Photography" (with demonstrations and mo- 
tion pictures), Dr. C. E. K. Mees, Vice-P resident in 
Charge of Research, Eastman Kodak Co., Rochester, 

N. Y. 



9:00 a. m. 



Tuesday, October 13th 

Buses will be at the Sagamore Hotel to transport mem- 
bers and guests to the Kodak Research Laboratories 
at Kodak Park. 



10:00 a. m.- 1:00 p. m. 



Technical papers program in the auditorium of the 
Kodak Research Laboratories. 



Sept., 1936] FALL CONVENTION 357 

1:10 p. m. Invitation luncheon at Kodak Park Works of Eastman 

Kodak Co. 

2:00 p. m.-5:00 p. m. Inspection tour of Kodak Park and the Kodak Re- 
search Laboratories. 

The program for the evening of this day will be announced 
in a later issue of the JOURNAL. 

Wednesday, October 14th 

10:00 a. m.-12:30 m. Sagamore Hotel Roof 

Technical papers program. 

1:10 p.m. Invitation luncheon at Bausch & Lomb Optical Co. 

Transportation to the Bausch & Lomb plant will be 
provided. Buses will leave the Sagamore at 12:30 
P.M. sharp. 

2:00 p. m.-5:00 p. m. Inspection tour of the Bausch & Lomb plant. 

7:30 p. m. Oak Hill Country Club 

Semi-Annual Banquet and Dance of the S. M. P. E. : 
addresses and entertainment. Motor-coach trans- 
portation will be provided to and from the Club by 
the Transportation Committee. Coaches will 
leave the Hotel promptly at 7:00 P.M. 



Thursday, October 15th 

10:00 a. m.-12:00 p. m. Sagamore Hotel Roof 

Technical papers program 

2:00 p. m. Technical papers program 

Society business 
Adjournment of Convention 

APPARATUS EXHIBIT 

There will be no general apparatus exhibit because of the limited display space 
at the Convention headquarters. The Papers Committee, however, is arranging 
to hold the usual Apparatus Symposium, and would like to be notified of anv 
papers for this session. 

POINTS OF INTEREST 

The University of Rochester. The University occupies two sites, the original 
location between Prince and Goodman Streets on University Avenue, and the 
River Campus in the southwest section of the city. For nearly seventy years 
after its organization the University was operated as a Liberal Arts College, but 
in 1918 the School of Music was organized through the generosity of the late 



358 FALL CONVENTION [j. s. M. p. E. 

George Eastman, and the school now bears his name. In 1921 it occupied modern 
buildings in the downtown section of the city, including the beautiful Eastman 
Theater. This theater is one of the chief cultural centers of the city, being the 
home of the Rochester Philharmonic Orchestra and the Civic Orchestra, and 
being the scene of many other musical and dramatic events. 

In 1920 the School of Medicine and Dentistry was organized with a generous 
endowment provided largely by Mr. Eastman and the General Education Board. 

The Bausch & Lomb Memorial Laboratory, housing the Department of 
Physics and the Institute of Optics, is located on the River Campus. This 
Institute was organized through the cooperation of Rochester optical industries, 
for the purpose of providing a center of teaching and research in the field of 
optics. 

The total enrollment of all departments of the University exceeds 4000 
students. 

The Genesee River. At the south edge of the city the river connects with the 
New York State Barge Canal. A barge channel is maintained to the center of 
the city at the Court Street dam. Below the dam the river enters a rocky bed 
and passes over five waterfalls having a total drop of 267 feet. These falls 
supply 50,000 horsepower to the city's industries. At the foot of the falls the 
river enters a deep gorge, through which it flows to its mouth on Lake Ontario, 
seven miles north of the business district. A drive north on St. Paul Street 
along the river to Veterans' Memorial Bridge which spans the gorge, and then 
across the bridge and north on Lake Avenue to the lake will be well worth while. 
Two city parks, Maplewood and Seneca, occupy opposite banks of the gorge near 
the Veterans' Bridge. Ontario Beach Park at the north end of Lake Avenue has 
a fine public bathing beach. 

East Avenue. This is one of the finest residential streets in this part of the 
country, extending from the downtown district east and south to Pittsford. 
At 900 East Avenue is located the former home of George Eastman, bequeathed 
by him to the University and now occupied by the President of the University of 
Rochester. 

Colgate- Rochester Divinity School. The campus is situated on a beautiful hill 
adjacent to Highland Park. It consists of a group of fine modern buildings 
grouped around the Divinity Tower, a dominating feature of the landscape. This 
school, organized in 1928 by the Baptist Education Society, combines and con- 
tinues the activities of the Colgate Theological Seminary, formerly of Hamilton, 
N. Y., and the former Rochester Theological Seminary. About 100 students are 
enrolled. 

Durand Eastman Park. This beautiful park extends for two miles along the 
shores of Lake Ontario and extends back through rolling hills covered with trees 
and flowers of many varieties. There is a bathing beach and public golf course. 
The park is reached by driving north on Culver Road to the park entrance. 

Genesee Valley Park. Located along the river adjacent to the River Campus 
of the University. Contains a public golf course, playgrounds, and picnic sites. 

Highland Park. A few minutes drive from the River Campus (east on Elm wood 



Sept., 1936] FALL CONVENTION 359 

to Goodman, north to the park). Contains 3900 varieties of trees, shrubs, and 
perennials. Particularly noted for its display of lilacs, peonies, and azaleas. 

Mendon Ponds Park. A few miles southeast of the city, reached over routes 
15 and 65. The site of an old camping ground of the armies of the expedition 
against the Seneca Indians. Contains three ponds, bridle trails, and picnic 
grounds. 

Powder Mill Park. On the site of an old, carefully hidden powder mill. Con- 
tains a trout fish hatchery, and is a favorite picnic site. Located fifteen miles 
east of the city on route 15. 

Letchworth Park. Located on the upper Genesee River about 50 miles south 
of Rochester. Contains some of the most notable waterfalls and river-gorge 
scenery in the eastern United States. Roads and foot-trails lead to three large 
falls, along the edge of deep rocky gorges and the deep wooded canyon below the 
falls. Picnic sites of unusual beauty abound, and there are cabins for the over- 
night visitor. Take routes 35-253-36-245. 

The Finger Lake Region. This famous scenic region of lakes, hills, and water- 
falls lies within an hour's drive to the south and east of Rochester, and offers 
dozens of motor trips through country of unusual beauty. There are six large 
lakes, the two largest of which, Seneca Lake and Cayuga Lake, are nearly forty 
miles in length. They are surrounded by wooded hills which rise to an altitude of 
2300 feet. There are nine state parks covering an area of 5000 acres and con- 
taining 1000 waterfalls and many scenic gorges. Visitors driving from Rochester 
to Ithaca will pass through the heart of the region. Several routes may be 
chosen passing through points of particular interest. Information and road 
maps for this trip may be obtained at the registration desk, where there will also 
be available maps for those wishing to plan more extended trips. 

Niagara Falls. Ninety miles west of Rochester. May be reached over 
route 104. 



SOCIETY ANNOUNCEMENTS 

FALL, 1936, CONVENTION AT ROCHESTER, OCTOBER 12TH-15TH, 

INCLUSIVE 

Details concerning the approaching Convention at Rochester, beginning Octo- 
ber 12th, will be found on page 353 of this issue of the JOURNAL, and at the foot 
of the inside front cover page. 



NOMINATIONS FOR OFFICERS FOR 1937 

About the time this issue of the JOURNAL is mailed to the membership of the 
Society, ballots will also be mailed for voting upon the nominees listed below for 
office for 1937. These nominations were completed at the meeting of the Board 
of Governors held at New York on July 10th : 

President: S. K. Wolf 

Executive Vice-P resident: H. G. Tasker 

Editorial Vice-P resident: J. I. Crabtree 

Convention Vice-President: W. C. Kunzmann 

Secretary: J. Frank, Jr. 

Treasurer: L. W. Davee 

Governors: M. C. Batsel 

J. C. Burnett 

A. N. Goldsmith 

J. L. Spence 

Provision is made in the ballot also for voting for other than those named. Two 
of the four nominees for the office of Governor are to be elected. 



SECTIONAL COMMITTEE 

As representative of the Sectional Committee on Motion Pictures, ASA, Mr. 
S. K. Wolf, Executive Vice-President of the SMPE, has been appointed to attend 
the meeting of the International Standards Association at Budapest on Septem- 
ber 3rd and 4th. Delegates from the nineteen national standardizing member- 
bodies of the ISA will attend the meeting, and it is hoped that an agreement will 
be reached in the matter of 16-mm. sound-film standardization, so that the diffi- 
culties resulting from the existence of the two standards, the SMPE and the 
DIN, may be overcome. 

In addition, steps will be taken toward standardization in the 35-mm. field, 
which it is expected will not present any considerable difficulty. 
360 



SOCIETY ANNOUNCEMENTS 
ADMISSIONS COMMITTEE 



361 



At a recent meeting of the Admissions Committee, at the General Office of the 
Society, the following applicants for membership were admitted to the Associate 
grade: 



ARGUELLES, E. 
2 Poniente 510 

Puebla, Pue., Mexico. 

BAHLER, W. H. 

Eastman Kodak Co. 
Rochester, N. Y. 

BAPTISTA, C. O. 
308 S. Wabash 
Chicago, 111. 

BARKER, H. G. 

149 Fountain Road 
Tooting, S. W. 17 
London, England 

BERG, A. 

1835 Burnside Ave. 
Los Angeles, Calif. 

BOLTON, A. C. J. 
1, Edward Road 
Chadwell Heath Essex 
London, England 

BOOTH, F. 
5, West Meade 

Swinton Lanes, England 

BOUZEMBERG, A. 

c/o French Line 
610 Fifth Ave. 
New York, N. Y. 

DARBY, A. W. 
39, Levendale Road 
Forest Hill 
London, S. E. 23, England 

FRANCK, E. W. 
299 Pacific St. 
Paterson, N. J. 

HAMANN, C. E. 

General Electric Co. 
1285 Boston Ave. 
Bridgeport, Conn. 



HAYSLETT, L. E. 

The Rudolph Wurlitzer Mfg. Co. 
North Tonawanda, N. Y. 

HOLLAND, G. E. 

1935 Biltmore St. N.W. 
Washington, D. C. 

HORNER, F. W. 

614 Upper Mt. Ave. 
Upper Montclair, N. J. 

HOVER, T. P. 
410 Marian Ave. 
Lima, Ohio 

KNECHTEL, L. 

George Humphries & Co. 
71 Whitfield St. 
London, W. 1, England 

LENARD, A. 

Pozsonyi ut 7.II.1 
Budapest, Hungary 

LEWIS, N. B. 

c/o Kodak (Australasia) Pty., Ltd. 
Abbotsford, N. 9, Victoria 
Australia. 

Lo, T. Y. 

Cinema Dept. of Army 
Affairs Committee 
Wuchang, China 

POPE, J. 

7402 Chappell Ave. 
Chicago, 111. 

ROSSIRE, H. McC. 
317 S. Sherbourne Dr. 
Los Angeles, Calif. 

RUTHERFORD, G. 
30 Highcroft Road 
Toronto, Canada 



362 SOCIETY ANNOUNCEMENTS 

SHAKEN, W. B. THOMPSON, R. H. 

P. O. Box 443 4245 Riverton Ave. 

Wallaceburg, Ontario, Canada North Hollywood, Calif. 

SILSBEE, B. F. VETCH, A. 

Chevrolet Motor Co. 1433 Silver Lake Blvd. 

Union & Natural Bridges Aves. Los Angeles, Calif. 
St. Louis, Mo. 

SLIVKA, F. X. WILLIAMS, R. H. 

P. O. Box 1777 Embassy Theatre 

Plaza Station Castlereagh St. 

St. Louis, Mo. Sydney, N.S.W., Australia 

In addition, the following applicants have recently been admitted by vote of 
the Board of Governors to the Active grade : 

GRUNAU, A. SARGENT, R. 

2511 W. Aubert Ave. Automatic Film Laboratories, Ltd. 

Chicago, 111. 513-515 Bowling St. 

HILDEBRAND, J. G., JR. Moore Park 

857 Boylston St. Sydney, N.S.W., Australia 
Boston, Mass. 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXVII OCTOBER, 1936 Number 4 



CONTENTS 

Page 

The Photoelectric Cell and Its Method of Operation 

M. F. JAMIESON, T. E. SHEA AND P. H. PIERCE 365 

Recent Advances in the Acoustical Design of Motion Picture 
Theaters S. K. WOLF AND C. C. POTWIN 386 

Analysis of Sound Waves H. H. HALL 396 

The Technical Basis of X-Ray Motion Picture Photography. . . 

R. JANKER 409 

A Film Emulsion for Making Direct Duplicates in a Single Step 

W. EARTH 419 

The Business Screen Some Demands Made by and upon It ... 

W. F. KRUSE 431 
New Motion Picture Apparatus 

1000- Watt 16-Mm. Filmosound Projector 

R. F. MITCHELL AND W. L. HERD 440 
Kodascope Model E. . A. E. SCHUBERT AND H. C. WELLMAN 447 

Symposium on the Slide-Film : 

Improvements in Slide-Film Projectors MARIE WITHAM 451 

Developments in Sound Slide-Film Equipment 

F. FREIMANN 455 

The Department of Agriculture's Experience in the Prepara- 
tion and Use of Slide-Films C. H. HANSON 460 

Joint Discussion 463 

Committees of the Society 466 

Rochester Convention, October 12th-15th, Inclusive 

General 471 

Tentative Program 476 

Abstracts of Papers and Presentations 480 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors . 
J. I. CRABTREE, Chairman 

O. M. GLUNT A. C. HARDY L. A. JONES 

G. E. MATTHEWS 



Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscriptions or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 

Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1936, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is 
not responsible for statements made by authors. 



Officers of the Society 

President: HOMER G. TASKER, Universal City, Calif. 

Past-President: ALFRED N. GOLDSMITH, 444 Madison Ave., New York, N. Y. 
Executive Vice-President: SIDNEY K. WOLF, 250 W. 57th St., New York, N. Y. 
Engineering Vice-President: LOYD A. JONES, Kodak Park, Rochester, N. Y. 
Editorial Vice-President: JOHN I. CRABTREE, Kodak Park, Rochester, N. Y. 
Financial Vice-President: OMER M. GLUNT, 463 West St., New York, N. Y. 
Convention Vice-President : WILLIAM C. KUNZMANN, Box 6087, Cleveland, Ohio. 
Secretary: JOHN H. KURLANDER, 2 Clearfield Ave., Bloomfield, N. J. 
Treasurer: TIMOTHY E. SHEA, 463 West St., New York, N. Y. 

Governors 

MAX C. BATSEL, Front & Market Sts., Camden, N. J. 

LAWRENCE W. DAVEE, 250 W. 57th St., New York, N. Y. 

ARTHUR S. DICKINSON, 28 W. 44th St., New York, N. Y. 

HERBERT GRIFFIN, 90 Gold St., New York, N. Y. 

ARTHUR C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

EMERY HUSE, 6706 Santa Monica Blvd., Hollywood, Calif. 

GERALD F. RACKETT, 823 N. Seward St., Hollywood, Calif. 

CARRINGTON H. STONE, 205 W. Wacker Drive, Chicago, 111. 



See p. 466 for Technical Committees 



THE PHOTOELECTRIC CELL AND ITS METHOD OF 
OPERATION* 



M. F. JAMIESON, T. E. SHEA, AND P. H. PIERCE** 

Summary. A simple description of the laws, governing the release of electrons 
from photoelectric surfaces, their collection at anodes, and the creation of ions in 
photoelectric cell gases by the "ionization" process, and questions of spectral selec- 
tivity of various photoelectric surfaces, the influence of spectral characteristics of 
illumination, and the dynamic characteristics of vacuum and gas-filled cells. 

Of all the many types of vacuum tubes associated with the repro- 
duction of sound-on-film motion pictures, the tubes that appear to 
be the simplest from an electrical point of view and, off-hand, one 
would also say from the manufacturing point of view are the photo- 
electric cells. However, the fundamental theory of operation of the 
cell presents some of the most perplexing problems of atomic physics, 
and its manufacturing success depends upon unbelievably delicate 
and accurate proportioning of materials and extremely closely con- 
trolled activation processes. 

So, despite its apparent simplicity, questions often occur to the 
user of photocells that are difficult to answer unless the fundamental 
characteristics are fairly well understood. With these facts in mind 
it seems as if there were considerable justification for bringing to- 
gether some of the fundamental information concerning photo- 
electricity, and that real benefit might result from an informal dis- 
cussion of the problems that have arisen and have been met in 
developing and applying this important adjunct to the field of sound 
pictures. This, then, is the object of this paper. 

THE PHYSICS OF PHOTOELECTRIC EMISSION FROM METALS 

Consider the atomic theory of the composition of matter, which 
pictures all matter as made up of sub-microscopic planetary systems 
called atoms, held together by inter-atomic forces of attraction and 
forming physical materials as we know them. Further, consider the 



* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Bell Telephone Laboratories, Inc., New York, N. Y. 



365 



366 JAMIESON, SHEA, AND PIERCE [j. s. M. p. E. 

atom divided into smaller particles carrying electrical charges, ar- 
ranged in the fashion of miniature solar systems with a positively 
charged proton or nuclear particle at the center, around which nega- 
tively charged electrons rotate in regularly denned orbits. 

In a gas the atoms are quite widely separated. In a conducting 
metal the spacing is so small that the outermost, or valence, electrons 
of any one atomic system find themselves almost as free to move into 
adjoining atomic systems as to remain in their original galaxies. 
This is the atomic theory of electrical conduction. Thus, an elec- 
trically conducting metal contains a great many electrons that drift 
freely from one atom to another and can be directed in their drift by 
an externally applied force. 

It seems quite plausible that a "free," or valence, electron, when it 
is deep within the metal, experiences almost balanced forces of at- 
traction, surrounded as it is upon every side by exactly similar atomic 
systems. As it approaches the surface of the metal, however, it en- 
counters quite a different situation. Upon one side of the surface 
the closely packed atoms of the metal exert a stronger force of at- 
traction for the electron than do the forces contributed by the more 
widely separated atoms of the outside atmosphere. Therefore, un- 
less the electron has acquired some additional energy of motion, or 
kinetic energy, it will not be able to cross the boundary at the sur- 
face, but will stay within the metal. 

This additional kinetic energy required to carry the electron across 
the surface boundary, since it is dependent upon the relative density 
or packing of the atoms, will vary as the relative density varies, and 
will thus be different for different metals and will be characteristic 
of the particular metal in question. 

If a negatively charged particle is subjected to the influence of an 
electric field, it will be attracted toward the region of more positive 
or higher potential. Upon moving toward the higher potential it 
will gain energy of motion or kinetic energy. If a moving electron is 
projected into a field in the direction opposite that in which it would 
normally move if starting from rest, it will be slowed down or will 
lose kinetic energy. Whether work is done upon the field by the 
charged particle, or upon the charged particle by the field, the energy 
can be expressed in terms of the voltage or difference of potential 
through which the particle moves. 

In a similar manner, an electron that has gained enough kinetic 
energy from the effect of light falling upon the metal to carry the 



Oct., 1936] PHOTOELECTRIC CELL, METHOD OF OPERATION 367 

electron across the surface boundary, loses a part of its kinetic energy 
in crossing the boundary, and the loss of energy can be expressed by 
an equivalent voltage. As was mentioned in a previous paragraph, 
this energy loss depends upon the particular metal in question, and 
the equivalent voltage is known as the work function of the particular 
metal surface and is generally denoted by <I>. A list of work func- 
tions for various metals is given in Table I. 





TABLE I 




Work Functions 


and Photoelectric Thresholds 


of Various Metals 




Work Function 


Photoelectric Threshold 


Metal 


(Volts) 


(Angstrom Units) 


Barium 


1.76 to 2. 29 


7000 to 5400 


Potassium 


1.76 to 2. 25 


6700 to 5500 


Rubidium 


1.8 to2.2 


6800 to 5700 


Caesium 


1.9 


6400 


Sodium 


1.9 to 2. 46 


6400 to 5000 


Lithium 


2.1 to2.9 


5800 to 4300 


Strontium 


2.3 


6000 


Calcium 


2.7 


4475 


Zinc 


3.32 


3720 


Copper 


4.1 to 4. 4 


3000 to 2750 


Tungsten 


4.58 


2700 


Iron 


4.7 


2620 


Silver 


4.73 


2610 


Gold 


4.82 


2650 


Nickel 


5.01 


2463 


Platinum 


6.3 


1962 



Several ways are known of supplying the additional kinetic energy 
to the free electrons of a metal to enable them to cross the surface 
boundary. One of the most familiar ways is to heat the metal and 
thus increase the thermal energy of the electrons and cause emission, 
as is done in the filament of a vacuum tube. The method in which 
we are most interested in this paper is that of imparting the additional 
energy by illuminating the metal surface. 

Light radiation has been assumed to consist of discrete bundles of 
energy called quanta. Einstein's expression for the energy imparted 
to the electron is 

* mv* = hv - $ 
where mv*/2 is the kinetic energy of a particle of mass m moving 



368 JAMIESON, SHEA, AND PIERCE [j. s. M. p. E. 

with a velocity v; hv is the quantum of energy, which depends in 
value upon the frequency v of the radiator, and <3> is the work function 
of the surface. 

This expression gives us the kinetic energy of a photoelectron after 
emission, and states that the kinetic energy of such an electron is 
equal to the energy of the light quantum less the energy lost by the 
electron in crossing the boundary of the surface. 

An important consequence of this analytical expression is the fact 
that as v, the frequency of the radiation, decreases, a point is reached 
where hv $ is exactly zero, which means that no kinetic energy is 
left after the electron crosses the boundary, so that it is held at the 
surface of the metal. Therefore, a threshold frequency must exist 
such that light of a higher frequency will cause photoemission, whereas 
light of a lower frequency will not. Such a threshold frequency 
has been experimentally found to exist exactly in accordance with 
the equation, and values of this threshold are given in Table I. 

So far we have considered only pure metals in bulk. Thin films 
of metals deposited upon glass or other conducting metals; surfaces 
activated by the deposition of surface layers such as the hydride of 
the metal formed by passing an electrical discharge through hydrogen 
to the cathode; and an interesting group of surfaces formed by de- 
positing a layer of dielectric material such as sulfur, or a layer of 
water vapor which reacts with the metal, or a treatment with an 
organic dye material ; present theoretical problems of a very complex 
nature, but in many cases produce photosensitive surfaces many 
times more sensitive than bulk metals. Such a surface layer results 
in the motion of the threshold frequency toward the red end of the 
spectrum and a greatly enhanced response to visible light. 

Still another type of surface, or possibly a modification of an al- 
ready mentioned type, consists of a composite mixture of three or 
more components, such as a base or bulk metal, oxides of this bulk 
metal, a second metal and possibly its oxide, all intimately associated 
in a complex surface matrix. 

Consistent with the above-described theory are the following laws, 
derived empirically : 

(1) The number of electrons released per unit of time by a photoemissive 
surface bears a direct proportionality to the intensity of the incident light. 

(2) The maximum energy of the released electrons is not dependent upon the 
intensity of the incident light but is directly proportional to the frequency of the 
light. 



Oct., 1936] 



PHOTOELECTRIC CELL, METHOD OF OPERATION 369 



RELATIVE EMISSION FROM VARIOUS MATERIALS 

Physics has classified light as a wave motion in the ether. As such 
it takes its place among the rest of electromagnetic radiations as 
part of an extensive spectrum which with the exception of only a very 
few narrow regions has been studied; from cosmic rays as short as 
10 ~ 12 centimeter continuously up through radio waves as long as 
22,000 meters. The part of this radiation spectrum that affects the 
eye, known as visible light, occupies a very narrow portion of the 
whole spectrum, as shown graphically in Fig. 1. 

The spectroscope has given us a great deal of information regarding 
the synthesis of light, because it makes possible the resolution of 
light into its various frequency components. A spark between metal 



S2 H 



O 




10 10 

WAVELENGTH IN CM. 

FIG. 1. The electromagnetic radiation spectrum. 



10 



electrodes becomes a series of sharply denned differently colored 
lines. Electrical discharges through gases at low pressure, such as 
we see in present-day neon signs, also exhibit characteristic bright- 
line spectra, as does also the naming portion of an arc between two 
electrodes. An incandescent metal source, such as a heated filament 
or the heated portion of the electrodes of an arc, on the other hand, 
radiates a so-called continuous spectrum, a continuous band of color 
ranging from the deep red end through red, orange, yellow, green, 
blue, indigo, and violet. Glass will not transmit frequencies corre- 
sponding to radiation in the ultraviolet, so if photoelectric surfaces 
are enclosed in glass bulbs they will not respond to ultraviolet radia- 
tion. On the other end, toward the infrared, glass is somewhat better, 
extending up to about 1 1,500 or 12,000 A, so that incandescent sources 



370 



JAMIESON, SHEA, AND PIERCE 



[J. S. M. P. E. 



or gaseous discharges even though enclosed in glass will radiate a 
considerable band of infrared radiation, and photoelectric cells that 
will respond in the infrared can be inclosed in glass and still be fairly 
effective. 

The light-source used for a particular photoelectric application 
can therefore be chosen, knowing its spectral characteristics, provided 
the characteristics of the photoemissive surface are also known. In- 
candescent metals, although radiating continuous spectra, do not 



400 




1500 



1000 



500 



5000 6000 7000 

WAVELENGTHS IN ANGSTROM UNITS 



0000 



YVAWL.l_c.iNVj i no IIN ^MNVJO i r\^ivi wrvt i M 

FIG. 2. Relative response of pure alkali metals to light of equal 
energy at various wavelengths. 

radiate all frequencies equally strongly, as will be shown later in this 
section. 

The source to be used thus depends upon the particular part of the 
spectrum desired. The basis of selection is the relative response to 
different parts of the spectrum exhibited by the particular photo- 
emissive material to be used. 

Photoelectric emitters do not respond with equal intensity to all 
wavelengths, but respond more readily and more strongly to radia- 
tion of particular wavelengths. Besides having, as we have seen, a 
characteristic cut-off or threshold wavelength beyond which the sur- 



Oct., 1936] PHOTOELECTRIC CELL, METHOD OF OPERATION 371 



100 



75 



50 



25 



K . LOCUS, OF SHIFT OF 
^MAXIMUM ACCORDING TO 



/VIENS DISPLACEMENT LAW 
. X MAX x T = 294 x K> 8 




2000 4000 6000 8000 10000 12000 14000 16000 16000 20000 

WAVELENGTH IN ANGSTROMS 



BLACK BODY 
AT 2644* K 



COLOR TEMPERATURE 271 
TRUE TEMPERATURE 2644*K 




15000 



21000 



27000 



FIG . 3 . ( Upper) Spectral distribution of radiant energy from ' ' black body ' ' 

at various temperatures. 

FIG. 4. (Lower) Comparison of spectral distribution of radiant energy 
from black body and from tungsten at same true temperature. 



372 



JAMIESON, SHEA, AND PIERCE 



[J. S.M. P. E. 



face is not photoactive, each particular surface has in general a 
different response characteristic. Curves of the color-sensitivity of 
the alkali metals that respond to visible radiation are shown in Fig. 2, 
where the ordinates represent the relative response to radiation of 
equal intensity throughout the spectrum and the abscissas represent 
the wavelengths of the radiation throughout the visible spectrum, 

with the approximate colors given below 
the wavelength scale. These curves, 
which are for mass metals, show relative 
response to equal amounts of energy at 
the various wavelengths. 

The variation of intensity from con- 
tinuous spectra due to incandescent metal 
sources can be accurately computed by 
the laws of radiation developed by 
statistical physics. An ideal radiator or 
"black- body" radiator is defined as a 
radiating material body capable of ab- 
sorbing or radiating all frequencies. 
Radiation from such a black body varies 
in intensity depending upon its tem- 
perature, in accordance with definite laws. 
Typical radiation intensity curves for 
such a black body at various tempera- 
tures are shown in Fig. 3. 

Incandescent metals depart slightly 
from ideal radiators or black bodies, 
since they do not in general absorb or 
radiate all frequencies. The distribution 
of energy from heated tungsten, for 
instance, compared to that for an ideal 
black body heated to the same true temperature is shown in the 
curves of Fig. 4. It will be seen from these curves that not only 
is the energy lower throughout the spectrum than that of the ideal 
radiator, but the position of the maximum-energy peak is shifted 
toward the short wavelength or blue end of the spectrum. 

If the response curves of Fig. 2 were plotted, not to equal energy, 
but in terms of the response to the energy from a tungsten light- 
source operating at a known color-temperature, they will show which 
surfaces are most sensitive to light from a heated tungsten source. 



110 


POT 

/ 


KSSIUK 


HYDR 


E7 


H 

r 

O 90 

_J 

5ao 


^ 
i RE 
1 OF 
M < 
1 
1 
1 


LATIVE 
TUNG 

:OLOR 

2710 


ENER( 
STEM t 
TEMP. 

JVS 


I 


/ 


r 
r 

0.0 

U 

r 

ft ,, 


1 1 
I 1 
I | 




/ 




t 
I 

I 




/ 









/ 




\ 

\ 


/ 






RELATIVE RE, 

L_8_1_J 


I 
1 
l 


/ 






1 


/ 






L;/ 


I 








fefk 







4000 5000 6000 7000 8000 

FIG. 5. Comparison of 
relative response of potas- 
sium hydride and alkali me- 
tals to tungsten light; color 
temperature, 2710K. 



Oct., 1936] PHOTOELECTRIC CELL, METHOD OF OPERATION 373 

This has been done in Fig. 5, along with the curve of the relative 
energy distribution of the source. 

If, instead of the bulk metals, we have a composite surface such as 
potassium hydride, the reponse of the surface so formed when plotted 
in terms of the energy from a tungsten light is seen to be much greater 
than that of any of the bulk metals. The dotted curve of Fig. 5 
is the response for such a potassium hydride surface. Potassium 
hydride was the material used in the first talking picture applications 





FIG. 6. 3-A photoelectric cell. 

because until very recently it was the most efficient emitter when 
used with a tungsten lamp as a light-source. 

The relative sensitivities of photoelectric cells are usually expressed 
in terms of the number of microamperes of current that the cell 
will produce when one lumen of light falls upon the cathode. A 
lumen is a unit expressing quantity of light, and is defined as the 
quantity that falls upon one square-foot of surface from a point- 
source of one candle-power one foot from the surface. 

Since the current that a cell produces is proportional to the number 
of lumens of illumination, it can be increased either (1) by increasing 
the size of the illuminated portion of the cathode, (2) by increasing 



374 JAMIESON, SHEA, AND PIERCE [j. s. M. p. E. 

the horizontal candle-power of the light-source, or (5) by decreasing 
the effective distance of the cathode from the source. While increas- 
ing the intensity of light upon a small illuminated spot on the cathode 
theoretically increases the response, this method of increasing the 
response is open to the very real objection that the radiant energy 
may be increased to an intensity such as to overheat the particular 
small spot and drive some of the active material of the cathode 
away from that portion of the surface, and hence result in a diminu- 
tion of the sensitivity of the spot. More uniform results will be at- 
tained by using as large an illuminated surface as the physical di- 
mensions of the cathode will permit. Optical systems should there- 
fore be designed to project, not a sharp image of light upon the 
cathode, but rather a larger more diffused image, over a considerable 
area of the active cathode. The number of lumens will be the same 
in either case, but local overheating will be avoided. 

THE CS-O-AG PHOTOELECTRIC CELL 

This type of composite photoelectric surface was first mentioned 
in literature by Koller in 1928, and has been developed in the Bell 
Telephone Laboratories for use in the 3-A Western Electric photo- 
electric cell for talking motion picture applications. Its physical 
appearance is shown in Fig. 6. 

Physically, the active elements of the cell consist of a semi- 
cylindrical cathode of thin sheet silver and a nickel anode rod located 
at the axis of the cathode cylinder. The concave surface of the cath- 
ode is the photosensitive surface and is turned toward the source of 
illumination. In the finished cell it presents a matte surface, which 
ranges in color for different cells from an iridescent bluish gray to a 
chocolate brown. The remaining mechanical elements of the cell 
compose the "chemical factory" for the production of the caesium 
during the activation of the cell. 

The activation of the cell during manufacture consists in first 
"working up" the cathode surface, which is originally highly burn- 
ished 99.9 per cent fine silver, by alternately oxidizing and reducing 
the surface in a glow discharge in electrolytically generated oxygen, 
accomplished by first allowing the discharge to oxidize the silver by 
short glowing and then by holding the discharge long enough to 
heat up the thin silver sheet and decompose the silver oxide, which 
is relatively unstable at elevated temperatures. This process cleans 
the surface and produces a fine-grained matte texture. The cleaned 



Oct., 1936] PHOTOELECTRIC CELL, METHOD OF OPERATION 375 

and roughened surface is then given a carefully calibrated oxidation, 
the amount of which is controlled by discharging a calibrated con- 
denser through the oxygen. Each discharge deposits a known amount 
of oxide, the amount of which can be controlled by the number of 
times the condenser is discharged and by the pressure of the oxygen 
in the cell. Caesium is then generated by flashing a chemical pellet 
composed of caesium chromate and aluminum, contained in a thin 
molybdenum envelope forming a high-resistance link in a circuit 
that can be electrically coupled to a high-frequency coil external to 
the cell. The chemical constitution of the caesium pellet is such that 
once brought up to a certain elevated temperature, the chemical 
reaction supplies its own heat, similar to a thermite reaction, and the 
caesium that is formed is completely and quickly evolved as a heated 
vapor, which, because of its high vapor pressure, leaves the pill at 
once. The amount of caesium formed can be carefully controlled by 
accurately weighing the chemicals of which the pill is composed, 
and because of the high temperature of the reaction, all of it is shot 
out into the bulb as a heated vapor. This hot caesium is hot enough 
to elevate the temperature of the silver cathode should it strike it 
directly. Because of the unstable nature of silver oxide, some of it 
would break down into oxygen and metallic silver should such heating 
result. The vapor is, however, deflected by a suitably shaped de- 
flecting shield between the pill assembly and the cathode, and strikes 
the cool bulb at a point opposite the concave surface of the cathode, 
where it condenses and deposits. This heat shield also protects the 
silver cathode from direct radiation from the heated molybdenum 
pill envelope, which reaches incandescence from the vigorous chemical 
reaction of the pill. 

From the bulb surface, the condensed caesium is driven over to the 
silver oxide cathode surface by gently heating the bulb in a stream 
of hot air. The conventional radiation type of electric oven can not 
be used for this process, because by radiation from the hot oven 
winding it would heat the cathode more than it would the thin caesium 
film on the bulb, and hence decompose part of the carefully calibrated 
oxide surface before the caesium could be driven over to it where it 
could react. After the caesium is all on the cathode surface, the cell 
is heated still further, the caesium combines with the silver oxide, and 
a stable composite surface results, which is a colloidal mixture of 
caesium, caesium oxide, silver oxide, and finely divided silver reduced 
from the silver oxide. All the processes are carefully controlled, 



376 JAMIESON, SHEA, AND PIERCE [j. s. M. p. E. 

even to the time and temperature of the heating in the hot air stream, 
and the finished product is capable of very great uniformity despite 
its critical composition. 

When the process is correctly carried out, the resulting photo- 
sensitive surface possesses a work function that measures less than 
a volt; a relative response to equal energy, shown for a typical 3- A 
type of cell in Fig. 7, with a peak of maximum response in the infrared 
region at about 8000 A; and a microampere sensitivity of between 
40 and 60 microamperes per lumen when a light-source of tungsten 
at a color temperature of 2710K. is used. 

A glance at the relative energy curve for tungsten at this tempera- 
ture, Fig. 4, shows the energy maximum at about 10,500 A, and shows 
why this type of surface is so effective for use with a tungsten light- 
source such as is used in the sound picture exciter lamp: namely, 
because its region of greatest response lies in the region of greatest 
energy from the tungsten light. 

Fig. 7 shows the relative response of the Cs-O-Ag type of photo- 
electric cell compared with the potassium hydride cell, such as was 
used in the Western Electric 1-A and 2- A photoelectric cells, in terms 
of equal energy to indicate the actual positions of the spectral maxima. 
Fig. 8 shows the same data in terms of the energy from a tungsten 
filament light-source at a color temperature of 2710K. The superi- 
ority of the Cs-O-Ag surface such as is used in the Western Electric 
3- A cell is at once apparent. 

GAS-FILLED PHOTOELECTRIC CELLS 

Even using the higher sensitivity of the Cs-O-Ag surface, the 
current that can be drawn from a photoelectric cell at reasonable 
values of illumination and with reasonable areas of illuminated 
cathode, is still of the order of only a few microamperes. It is possible 
to increase this feeble current several-fold by filling the cell with some 
inert gas at a low pressure, which by ionization will provide addi- 
tional carriers of electricity. The kind of gas and the quantity of it 
are subject to critical limitations which should be understood by the 
user as well as the maker of photocells. 

Consider, then, an electron driven from the photoelectric surface 
by the additional energy imparted to it by a quantum of light. As 
the electron emerges from the surface of the metal cathode of the 
photoelectric cell, it possesses a certain amount of kinetic energy. 
This is supplemented by the energy that it gains from the action of the 



Oct., 1936] PHOTOELECTRIC CELL, METHOD OF OPERATION 377 

electric field between cathode and anode due to the external battery 
in the circuit. If the total energy of motion, or kinetic energy, reaches 
a certain definite value before the moving electron collides with a 
gas atom or molecule, the electron may collide with sufficient impact 
to knock out one of the electrons composing the atom. 

The net result of a collision between a photoelectron and a gas atom 
may be the presence of the electron that has been knocked loose from 
the atom; the original electron that did the knocking out, and was 
thereby deflected into a new path; and the atom that is now short 
one electron, and is thus carrying a charge that is effectively positive 
by the amount of the negative charge of the electron it has lost. 
Three electrically charged particles therefore exist and can be in- 
fluenced by the potential field established by a battery connected 
between cathode and anode; and if they reach the respective elec- 
trodes to which they are attracted because of their charges, they 
will result in a current three times as great as the current that would 
have resulted had the emerging electron gone directly from the 
cathode to the anode without colliding. 

The process of breaking loose one or more of the electrons from an 
atom is known as "ionization." The voltage denoting the energy 
necessary to tear loose an electron is known as the "ionizing potential" 
of the atom of the gas and, of course, may possess more than one value. 
That is, a certain voltage may represent the energy necessary to free 
one electron, another value may be that required to free two elec- 
trons, and so on. 

Three additional influences enter, which is the reason why it has 
been said that the resultant current "may" be three times as great. 
For example, in moving toward the cathode an atom with one or 
more electrons released by collision will encounter another electron 
either one freed from some other atom, or one of the electrons from 
the photoemissive surface which does not itself possess enough energy 
to tear free any more electrons; and since the ionized atom is effec- 
tively positively charged, it will possess an attractive force that may 
cause the electron that it has encountered to attach itself to the ion, 
electrically neutralizing it so that even though it may move as far as 
the cathode, it will no longer carry a charge and no additional current 
will result. This effect is known as "recombination." Another 
alternative may present itself if the ion, carrying its effective positive 
charge, is accelerated sufficiently by falling through the potential 
field so that it, too, acquires an energy equivalent to the ionization 



378 JAMIESON, SHEA, AND PIERCE [j. s. M. p. E. 

potential of the gas, and so that if it collides with another neutral 
gas atom it may do exactly the same thing that an electron with this 
energy does namely, ionize the atom with which it collides, forming 
new free electrons and other ions. Still a third alternative exists, 
due to the fact that ionized atoms may be accelerated sufficiently 
before striking the cathode so that they possess enough energy ac- 
tually to drive electrons from the metal of the cathode. The elec- 
trons so driven out are known as ' 'secondary" electrons, and the 
emission resulting as "secondary emission." 

All four of these effects are present in different degrees in a gas- 
filled photoelectric cell with a battery in the circuit (1) ionization 
by the photoelectrons, (2) ionization by the accelerated ions them- 
selves, (5) secondary emission from the ions striking the cathode, and 
(4) the opposing effect of recombination which in part neutralizes 
the effect of the other three processes. The resulting current in the 
external circuit is a complicated function of all four. 

Fig. 9 shows the current that results when a photoelectric cell is 
illuminated with a constant illumination and the voltage is varied 
across the electrodes. If the cell is a vacuum cell, the curve with 
the long flat portion results; that is, a voltage is reached (about 
twenty volts) at which all the photoelectrons emitted are made to 
travel across to the anode; and beyond that voltage the current can 
increase only very slightly because no more electrons are available. 
If gas is admitted into the cell, a different condition takes place. 
When the voltage reaches the p< 'nt at which some of the electrons 
can acquire an energy equivalent to 15.7 volts, the argon which is 
the gas used in this case is ionized by colliding photoelectrons 
and the current is no longer due only to photoemission. As the 
voltage is increased, more and more of the photoelectrons, and finally 
the ions themselves, produce additional ions and electrons, and the 
increase in current becomes greater and greater. If electrons or ions 
can acquire an energy of 47 volts, each may doubly ionize other gas 
atoms that is, knock out two electrons; and because of the low 
work function of the photoelectric surface itself, each ion that collides 
with it may possess enough energy to knock out, not one, but many 
electrons from the metal. A point is finally reached at which the 
ionization process becomes cumulative, and the photoelectrons are 
no longer necessary for carrying on the ionization, which so far exceeds 
recombination that the discharge becomes self-sustaining and con- 
tinues after the illumination is cut off. This condition is known as 



Oct., 1936] PHOTOELECTRIC CELL, METHOD OF OPERATION 379 

the "spark" condition, and the current in such a discharge will build 
up to a value limited only by the resistance of the battery and con- 
necting leads, or by the value of an external protective resistance 
in the circuit. Such protection is quite necessary, since the violent 



POTASSIUM 
HYDRIDE 




>-0-AG 




4000 5000 6000 7000 8000 9000 10000 1 1000 12000 
WAVELENGTH IN ANGSTRQM UNITS 




4000 5000 6000 7000 6000 9000 10000 11000 12000 

FIG. 7. ( Upper} Relative spectral response of potassium 
hydride and Cs-O-AG photocells to equal energy. 

FIG. 8. (Lower) Relative response of potassium hydride 
and Cs-O-AG photocells to tungsten light at color-tem- 
perature of 2710K. 



electrical spark or arc than can result at a high voltage would rapidly 
overheat the cathode and disintegrate the active surface. 

The point at which the self-sustaining discharge takes place, of 
course, depends upon the density of the gas in the cell; the density 
of the photoemission which starts it, i. e., the surface activity of the 
cell; or the intensity of the illumination; and to a lesser degree, 
upon the temperature of the cell. Also it depends upon the geometry 



380 



JAMIESON, SHEA, AND PIERCE 



IT. S. M. P. E. 





















1 
SPARKS 


AT 140 Vy 


























7 
























/ 


f 


u 

a. 
u 






















/ 




* 




















A 


SFIL 


LED 


| 
















X 


X 






















xX 


x^ 


















^ 


^ 


^^ 














Y^ 


















V- 


*cuu 


wj 




























f 










\ 


/OUT 


S 













100 110 120 130 



.5 MM. OF GAS 
SPARKS AT 79V 



05 MM. OF GAS 
SPARKS AT 155V 




10 20 30 40 50 60 70 60 90 100 110 I2O 



FIG. 9. (Upper) Current-voltage characteristics of argon-filled 
and vacuum Cs-O-AG cell of about the same surface sensitivity; 
0.05 lumen on 3 /4-inch circular window. 

FIG. 10. (Lower) Effect of gas pressure upon voltage-current 
characteristics of Cs-O-AG photoelectric cell at 0.05 lumen. 



Oct., 1936] PHOTOELECTRIC CELL, METHOD OF OPERATION 381 

of the elements of the cell, and upon the disposition and shape of the 
electrodes, etc. 

If the illumination of the photoelectric cell is interrupted, an inter- 
rupted output current will result. This is the basis for use of the cell 
in the reproduction of sound in talking motion picture applications. 
The varying density of the film sound-track is used to vary the 



13 
12 
II 
10 
9 

e 

7 
6 
5 
A 
3 
2 
I 

< 

Fi 












.5 MM / 
ARGON/ 


1 


' IMM 
ARGON 




/ 














/ 






.IMM / 
ARGON/ 
















/ 


1 




> 


//2MM 
JARGON 












1 


/ 






// 






M 











/ 


/ 




J 


7 


.05 MM 
ARGON/ 













It 


/ 




/ 




/ 


/ 


i 

?$ 








/ 


/ 




/ 




/ 


/ 




5 








1, 


/ 


/ 




/ 


s 












1 


7 


/ 




/ 








^ 








// 


/ 




X 






^ 


%ar 






/, 


'/ 


/ 


X 


rfX" 


^ 


x*" 1 "^ 










/ 


'// 


/ 


^ 
^ 


^ 
















f' 


'< 


^ 


















A 


^s' 








LI 


MEN 


s 










) .1 .2 .3 

3. 11. Response vs. illumination at various gas pres- 



sures, at 60 volts. 



illumination of the cell; and the magnitude of the current, which 
varies as a result of the change in illumination, can be amplified to 
produce a sound in a loud speaker. If faithful reproduction of the 
variation of intensity of the illumination passing through the film 
is desired, it is important, first, that the current through the photo- 
electric cell be linearly proportional to the illumination striking the 
cathode; that is, that the current will double when the illumination 
is doubled, or will halve when the illumination is halved. Experi- 
ment has determined, and empirical laws already stated show, that 



382 



JAMIESON, SHEA, AND PIERCE 



[J. S. M. p. E. 



the vacuum photocell possesses such a characteristic; but due to 
complexities in the ionization effects, the linear proportionality does 
not hold for gas-filled cells operated at higher voltages or high illumi- 
nations. The departure from linearity becomes greater, the higher 
the gas pressure in the cell up to a certain point, as gas ionization 
plays a greater and greater part in the resulting current. Fig. 10 
shows a family of voltage-current characteristics taken by varying 
the gas pressure in a cell fastened to the pumps so that the cell can 
be filled and pumped out, and the same surface conditions obtained 
for any gas pressure. Fig. 11 shows a similar family of curves 
for the same cell when the voltage is held constant and the illumi- 
nation intensity varied. The vacuum cell shows a linear response 
that is, even increments of illumination result in even increases 
in current. Gas-filled cells depart from this linear condition, the 



J I I I 



VACUUM CELL 
GAS FILLED 



FRE.QUE.NCY 



100 



5000 



FIG. 12. Effect of gas in a Cs-O-AG photoelectric cell in terms of re- 
sponse to frequency of modulation of the light. 

departure increasing with the pressure and passing through the same 
sort of maximum at 0.5-mm. argon pressure as did the voltage- 
current characteristics. 

Another effect enters due to the fact that the times required by 
electrons and ions to travel across the inter-electrode space depend 
upon the relative sizes of the particles. Electrons, being small, 
travel at higher velocities than do the ions, since for the same amount 
of energy their velocities are inversely proportional to their masses. 
The result is that as the light is interrupted or varied at higher and 
higher frequencies, the electrons still travel across well within the 
times of the variations, but the heavier and slower moving ions can 
not follow as well. If the cell is placed in a standard amplifier circuit 
and the magnitude of the response to light of different frequencies is 
measured, the result will give us a characteristic such as shown in the 
typical experimental set of curves of Fig. 12. The gas-filled cell 
lessens in response at the higher frequencies, the extent depending 



Oct., 1936] PHOTOELECTRIC CELL, METHOD OF OPERATION 383 

again upon the pressure of gas in the cell. The cell of Fig. 12 was 
one that had a relatively low pressure of argon, and the decrease 
in the response is less than that often encountered in cells containing 
higher pressures of argon. A decrease in response of only 0.7 db. at 
10,000 cps. is easily compensated for in the amplifier circuit. Higher 
pressures of argon, and consequently greater variation in response, 
may produce distortion that is less easily compensated for. A 
vacuum cell will not show this decrease until very high frequencies 
are attained. The normal circuit application is such that these higher 
frequencies can not be utilized anyhow, and are unimportant com- 
mercially. 

The lack of linearity of response vs. illumination, and this decrease 
in response with increase in frequency, give us two arguments for 
low gas pressures in the cell. Another important consideration 
intimately connected with the gas pressure in the cell concerns the 
voltage at which the cell sparks over. 

Arbitrarily, a voltage across the cell equal, roughly, to 75 per cent 
of the voltage at which the cell sparks over is chosen. Such a value 
brings the operation well below the unstable region of the character- 
istic, and allows reproducible and stable operation of the cell. 

Cells that show high values of response when tested in a test-set 
illuminating a large window area may, when subjected to an intense 
small-area illumination, show marked distortion characteristics due 
to being operated too closely to the spark potential of the cell. 

Cells operated with a greater part of the cathode illuminated can 
be operated under higher gas pressures than can cells in which a 
small intense spot of illumination is used. Thus, the conditions 
under which the cell is to operate will govern to a considerable 
extent the pressure to which the cell can be filled. 

Suffice it to say that careful selection of the argon pressure is of 
vital importance for sound picture applications in which lack of dis- 
tortion is important. Microamperes per lumen do not tell the whole 
story, and cells that give high response when measured either in a 
conventional sound picture amplifier or in a photometer set-up are 
not necessarily the most suitable for high-quality reproduction. 
Often cells that are sold to replace standard equipment spark only a 
few volts above the standard operating voltage, and will operate 
almost in the glow-discharge region, in which they are unstable. 
Low surface activities are often bolstered up to values as high as or 
higher than those found in good photoelectric cells, so that the cells 



384 JAMIESON, SHEA, AND PIERCE [J. S. M. p. E. 

appear very good when tested ; but the gas pressures necessary so to 
bolster up the response introduce difficulties in operation that are 
difficult to locate. Resistances in the amplifier input circuits may 
effectively so limit the current from the cell that no visible glow dis- 
charge is observed; but unstable operation can result without any 
visible glow being present. The importance of cells designed to oper- 
ate properly can not be overemphasized. 

DISCUSSION 

MR. TASKER: Does 0.05 argon pressure represent modern commercial prac- 
tice? 

MR. PIERCE: Yes. In the 3- A Western Electric photoelectric cell that is 
normally used, the pressure is about 0.04 mm. 

MR. KELLOG: I believe that the energy distribution curves showing the 
sensitivities of the several materials at various wavelengths were plotted on the 
basis of the energy radiated per unit difference in wavelength. It seems to me 
quite as logical, although perhaps not conventional, to plot the energy given off 
(or, if not the energy, then the current) per unit of difference in frequency instead 
of per unit difference in wavelength. It would also be possible to plot as ordinates 
the current per unit of difference in log frequency, or difference in log wavelength. 
This would be an intermediate type of curve. Each of the three ways of plotting 
the characteristic would make the maximum, or peak, occur at a different fre- 
quency. Of course, such curves are interconvertible, and so long as the scales 
are properly defined this should not lead to any confusion or misunderstanding; 
but the usual methods of plotting give decidedly different impressions. I was 
wondering whether there was any justification for one type over another. 

MR. SHEA: I think the only justification is what is useful in interpreting 
them. 

MR. CARLSON: Were the sensitivity curves shown for the different types of 
cells with tungsten filaments at various temperatures based upon the distribution 
of radiant energy from such sources as actually measured when enclosed in a 
glass envelope; or were they based upon the radiation as computed by Planck's 
formula? 

MR. PIERCE: They were based upon measurements of tubes enclosed in glass 
envelopes. 

MR. TASKER: The characteristic of all the gas-filled cells which, as Mr. 
Pierce says, gives rise to distortion, is, I suppose, somewhat controllable. The 
curve for distortion vs. coupling resistance between the cell and the succeeding 
parts of the circuit, for example, normally shows that the distortion is much 
higher for high coupling resistances than it is for low ones. I wonder whether 
that is merely a compensation that arises due to the fact that the applied potential 
passes through the same resistor referred to, so that as the current builds up, 
the potential applied to the cell becomes less; or would that give us an opposite 
effect? Why is it that there is less distortion with a lower coupling resistor? 

MR. PIERCE: There should be no distortion with a vacuum photoelectric 
cell caused by the drop in potential in the resistance used to supply the potential 



Oct., 1936] PHOTOELECTRIC CELL, METHOD OF OPERATION 385 

to the cell as well as to couple it to the amplifier tube. The current is practically 
independent of voltage, and is only a function of the illumination. In a gas cell, 
however, there may be distortion, caused by this potential drop, although not 
necessarily. In the gas cell the current-illumination curve for a fixed potential 
bends upward slightly with increasing illumination, and the current-voltage curve 
also bends upward with increasing voltage, so that the potential drop in the cou- 
pling resistance tends to compensate for the upward curvature of the current- 
illumination characteristic. A particular value of coupling resistance may give a 
straight-line dynamic characteristic with minimum distortion. 

In cells that are operated too near the flashing potential the current-voltage 
characteristic bends upward rapidly with increasing voltage, so that the slight 
curvature in the current-illumination characteristic is very much overcompen- 
sated by the drop of potential in the coupling resistance, thus giving a curvilinear 
dynamic characteristic with corresponding distortion. Under these conditions 
the higher the coupling resistance the greater the potential drop, and hence the 
greater the distortion. 

MR. CRABTREE : What happened when the tube began to glow at the critical 
voltage? Is the tube useless thereafter? 

MR. PIERCE: If the glow persists it would heat up the surface so that it 
would probably lose its activity. If it is allowed to persist for only a few minutes 
it does not affect it. 



RECENT ADVANCES IN THE ACOUSTICAL DESIGN OF 
MOTION PICTURE THEATERS* 



S. K. WOLF AND C. C. POTWIN** 

Summary. The various factors that must be considered in the acoustical design 
and treatment of theaters are outlined, as a guide to architects and engineers in solv- 
ing the more common problems arising in this particular phase of motion picture 
engineering. 

Fundamental considerations, such as proportions, shape, sound insulation, stage, 
etc., are briefly covered. The relation of "fixed" absorption to surf ace acoustic treat- 
ment is also discussed. Curves recommended by Electrical Research Products, Inc., 
showing optimal and percentage optimal reverberation times as functions of volume 
and frequency, respectively, are offered. Particular stress is placed upon the necessity 
of carefully selecting the materials for theater treatment with respect to their sound- 
absorbing efficiencies throughout the frequency range. 

Prior to the practical adaptation of sound recording and reproduc- 
ing systems to the motion picture industry, the architect was con- 
cerned chiefly with decorative treatment in theater design. Little 
consideration, if any, was given to general acoustic requirements. 
The legitimate theater placed certain limitations upon design, al- 
though, in most cases, acoustics were left to chance, in the anticipa- 
tion that the direct vocal and musical presentation would approach 
at least an acceptable standard of naturalness and intelligibility 
throughout the seating area. 

The era of classifying the talking picture as a novelty has long 
since passed. The public is now more conscious of the quality and 
naturalness of the sound accompanying the picture, and their ex- 
pectations in this respect are worthy of careful consideration in the 
technical field. How disappointing to an architect must be a patron's 
passing comment, "A beautiful theater; but the sound!" Such is 
frequently the case, however, even with the recent advances in theater 
acoustics. Architects and engineers must realize that good acoustic 
conditions are equally important to architectual and decorative treat- 
ment in theater design. The purpose of this paper is to outline briefly 

* Presented at the Fall, 1934, Meeting at New York. 
** Electrical Research Products, Inc., New York, N. Y. 

386 



ACOUSTICAL DESIGN OF THEATERS 387 

the fundamentals that must be considered in the present as well as in 
future acoustical design and treatment of theaters. 

DESIGN 

(1) Proportion and Shape. The area and relative dimensions of 
the lot upon which the theater is to be built are generally the limit- 
ing factors in this respect. The ideal proportions for the auditorium 
proper, and the ones that, as indicated by past experience, assure 
the most favorable distribution of sound energy, are of the order 
of 2:3:5 for the height, width, and length, respectively. This 
ratio is applicable to theaters having cubical contents ranging to 
approximately 500,000 cubic feet. Above this volume, the height 
would, for practical purposes, be less in its relation to the width and 
length. 

The square type of theater is acceptable but not fully practicable, 
from the standpoint of proper distribution and illusion for all sections 
of the seating area. The long and narrow type, sometimes called 
the "shooting gallery," should, when possible, be avoided. Difficul- 
ties arising from multiple sound reflections and inadequacy of dis- 
tribution are always present in this type. 

The importance of avoiding pronounced and unbroken curved 
surfaces such as domes, rear walls, and vaulted ceilings, particularly 
when the centers of curvature fall within the limits of the theater 
proper, can not be too strongly emphasized. Reflections of sound 
energy from such surfaces generally produce echos and areas of either 
excessive or deficient loudness. Only with the proper use of efficient 
sound-absorbing materials may such surfaces be incorporated in 
the design, although to eliminate them is far more practical. In 
cases where the intricacy of architecture requires the use of curved 
surfaces even to a moderate degree, a competent acoustic consultant 
should be retained to suggest such modifications in design as may be 
necessary to avoid possible defects. 

Non-parallelism of surfaces is an important consideration, par- 
ticularly in the design of small theaters. Side walls should preferably 
be angled slightly, so as to reduce cross-reflections or standing- wave 
patterns between these surfaces. Where balconies are not provided, 
the contour of the rear wall surface should be well broken. A ceiling 
"stepped" slightly in uniform flat planes from the proscenium opening 
to the rear wall is also desirable, particularly in small theater design. 

(2) Stage. The correct design and treatment of the stage are 



388 S. K. WOLF AND C. C. POTWIN [j. s. M. p. E. 

acoustic problems in themselves, and should be considered as care- 
fully as the acoustics of the auditorium proper. In addition to allow- 
ing ample distance between the screen and the first row of seats for 
good vision, suitable space must be provided between the rear of 
the screen and the stage rear wall for accommodation of horns, 
baffles, and other necessary equipment. In the theater used ex- 
clusively for motion pictures, the distance should preferably be not 
less than 6 feet, which allows ample space for suspending, tilting, and 
flaring the horns. 

The stage rear wall surface, in line with, and over an area at least 
approximating that of the screen, should preferably be of angular or 
staggered construction, to minimize the interference patterns fre- 
quently encountered when entirely flat surfaces are provided at this 
point. In theaters in which the distance between the screen and the 
stage rear wall is to exceed 10 feet, it is also frequently desirable to 
provide a drop of heavy weight-lined velour suspended behind the 
horns, of an area at least approximating that of the screen. The drop 
may be hung on lines, to be raised or drawn back, if necessary, to 
clear the stage for special presentations. It is generally desirable to 
indicate upon the drawings the requirements for the drop, although its 
ideal spacing behind the horns is best determined by a sound engineer 
when installing the horns and other equipment upon the stage. 
Suitable draping in the area between the side and top edges of the 
screen and the rear wall is also beneficial, particularly on large stages. 
The stage floor should in all cases be of heavy construction and well 
braced to prevent any possible resonance or vibration. 

(3) Construction. In densely populated areas and in locations 
where the theater would be subject to a high external noise level, care 
should be taken in design to avoid any masking effect produced by 
such interference. External noise may enter the theater via several 
channels : namely, the lobby, windows, and exit doors, if opened or 
of light construction, and through sound transmission caused by 
general vibration in the theater structure. The lobby should be 
separated as much as possible from the theater proper. All sections 
of the theater subject to external noise or vibration should be of 
heavy construction to minimize transmission through the building 
structure. 

The projection room should be sound-proof, as far as practicable, 
and the inner wall and ceiling surfaces of this unit treated with an 
efficient sound-absorbing material. 



Oct., 1936] ACOUSTICAL DESIGN OF THEATERS 

ARTICULATION AND INTELLIGIBILITY 



389 



(1) Reverberation Analysis. Having carefully considered the 
various phases of design affecting the acoustic condition, we must 
next determine, with all possible accuracy, the requirements of interior 




12 g 256 51? 102* 

FIG. 1. Absorption characteristics of theater seats and audience. 



Curve 

A 

B 
C 
D 

E 
F 



Back 

Wood 

Panel Leather 
Panel Velour 
Full Velour 
Full Mohair 
Full Mohair, 
on Springs 
Average Absorption of Individual 



Seat 
Wood 

Leather; Box Springs 

Velour; Box Springs 

Velour; Box Springs 

Mohair; Box Springs 

Mohair; Box Springs 



surface absorption for correctly reducing the reverberation, interfer- 
ing reflections, and echo. Several theoretical formulas have been 
derived for computing reverberation time, as determined by the 
absorption present in the theater, of which the most commonly used 
is the one developed by W. C. Sabine. 1 Formulas more recently 
developed are those of C. F. Eyring, 2 and W. J. Sette. 3 A correction 



390 



S. K. WOLF AND C. C. POTWIN 



[J. S. M. p. E. 



factor developed by V. O. Knudsen 4 takes into consideration air 
absorption as a function of the enclosed volume and humidity. These 
latter formulas have increased the accuracy of computation over that 
of the original Sabine formula, and their use is preferred from this 
standpoint. 

It is commonly known that the absorption present in a theater is a 
function of the type of seats, the percentage of seats occupied by the 
audience, and the quantity of carpets, drapes, and other absorbing 




1. 



10,000 100,000 1,000,000 2,000.000 

FIG. 2. Optimal reverberation time vs. volume, for reproduced sound at 

512 cps. 

materials. The use of highly upholstered seats is of particular value 
from an acoustic standpoint since, when unoccupied, they compensate 
to a large degree for absorption normally provided by the audience, 
and thereby assure a more uniform reverberation period for all varia- 
tions in attendance. The use of such seats also appreciably reduces 
the quantity of other types of absorbing materials required. Plain 
wooden seats provide negligible absorption in comparison to the 
audience, and the use of such seats generally necessitates the applica- 
tion of a large quantity of acoustic material to compensate for the 
inefficiency of the seats and assure a desirable acoustic condition for 
average audiences. This frequently results in a slightly "dead" 



Oct., 1936] 



ACOUSTICAL DESIGN OF THEATERS 



391 



condition, with maximum audiences, but still leaves the theater 
somewhat reverberant for small percentages of attendance. Fig. 1 
shows a comparison of the general efficiency and acoustic character- 
istics of seats of several different types, relative to the average absorp- 
tion characteristic of an individual present in the theater. These 
data are adopted from tests made by F. R. Watson 5 and W. C. Sabine. 
The seat tests were made only at the frequencies indicated. Extrapo- 
lation of the curves will give, within reasonable limits of accuracy, 
the relative absorption values at the other frequencies. From an 




1*8 256 512 

FIG. 3. Optimal reverberation-frequency characteristic, in per cent of re- 
verberation time at 512 cps. 

acoustic standpoint the effective volume per seat should preferably 
not exceed 150 cubic feet for the average theater. 

The carpet used in the theater should be of a heavy grade, rein- 
forced, which will effectively reduce impact noise as well as provide 
acoustic absorption. Drapes, such as those generally installed around 
doors, lobby openings, etc., should preferably be heavy lined velour. 

Having determined with all possible accuracy the total absorption 
contributed by the proposed seats, carpet, drapes, and other surfaces, 
and including the absorption provided by the probable average audi- 
ence (we assume two-thirds of the seating capacity when using efficient 
seats), the introduction of this figure into the formula as a function 
of the enclosed volume and associated constants will indicate, within 



392 S. K. WOLF AND C. C. POTWIN [j. s. M. p. E. 

reasonable limits of accuracy, the probable reverberation period of 
the proposed theater. This analysis should be made at octave in- 
tervals for frequencies ranging from at least 128 to 4096 cps. 

(2) Optimal Times of Reverberation. Fig. 2 shows an optimal 
reverberation time curve for reproduced sound at 512 cps., as recom- 
mended by Electrical Research Products, Inc., for theaters of satis- 
factory shape and proportions. Fig. 3 is a percentage curve which, 
applied to the optimal values of Fig. 2, will indicate the desirable 
reverberation time for frequencies other than 512 cycles per second. 
These optimal and relative percentage curves are based upon ex- 
tensive theoretical and practical research comprising instrumental 
measurements in theaters both treated and untreated, articulation 
tests, and general observations of sound quality by competent critics. 
A deviation of ==10 per cent from the optimum is permissible, al- 
though the time should not exceed these limits for reproduced sound. 
In theaters to be used for direct, as well as for reproduced sound, 
the optimal reverberation time selected should preferably approximate 
the upper 10 per cent limit indicated on the curve in Fig. 2. 

(3) Frequency Distortion. This is a factor that warrants careful 
consideration, because the results to be attained, at present as well 
as in the future, due to progressive improvements in sound repro- 
ducing systems, will depend largely upon the general acoustic char- 
acteristic of the theater. The use of materials that provide a large 
amount of absorption at the high frequencies and only a small amount 
at the low frequencies, as explained later under the section on selec- 
tion of materials, must be avoided unless they are to be used in con- 
junction with other types, the combination of which will produce 
the proper balance of absorption at all frequencies. The ear is less 
sensitive to low-frequency sounds than to high-frequency sounds; 
and, therefore, more reverberation is permissible at the low frequen- 
cies. This variation assumes certain definite limits, however, which 
must be maintained to avoid noticeable "boominess" at the low 
frequencies and excessive "deadness" throughout the higher portion 
of the frequency spectrum. Frequency distortion may be caused also 
by poor construction of the interior surfaces. If the surfaces are made 
of light-weight materials, they must be strongly braced to avoid pro- 
nounced resonance at certain frequencies. 

(4) Loudness. A level of operation consistent with good hearing 
conditions must be maintained throughout the entire seating area 
to assure the maximum degree of naturalness. Operating the sound 



Oct., 1936] ACOUSTICAL DESIGN OF THEATERS 393 

system at a high level increases the duration of reverberation and may 
cause distortion. To avoid these defects, all possible sources of in- 
ternal as well as external noise must be checked and eliminated as 
far as practicable. The most common sources of internal noise, 
other than those already considered, are ventilating equipment 
blowers, driving motors, fans; motor-generator sets; heating equip- 
ment; etc. Sound isolation of ventilating systems, motor-generators, 
and other equipment; lining ducts with efficient sound-absorbing 
material; and providing for insulative machinery bases where re- 
quired, are effective methods for reducing internal noise from these 
sources. 

SURFACE TREATMENT 

(1) Selection of Materials. The principal factors governing the 
selection of an acoustic material are (1) its characteristic, or absorp- 
tion over the frequency range relative to other types of absorption 
within the theater ; (2) its general efficiency for treatment of the sur- 
faces under consideration; and (5) its adaptability to the proposed 
architectural and decorative scheme. Numerous kinds of acoustic 
materials in the form of tiles, felts, plasters, etc., both fireproof and 
non-fireproof, have been developed within the past few years, pro- 
viding a variety sufficient to fulfill practically every requirement 
from both acoustic and architectural standpoints. Continual progress 
is being made in the further development of these as well as newer 
materials, improving their acoustic efficiency and adaptability to 
various types of construction. Through the medium of the Acoustic 
Materials Association, 6 information pertaining to the efficiency of 
the various kinds of materials supplied by the leading manufacturers 
is available without cost. From a comparison of these, as well as 
other data, a material or combination of materials can generally be 
selected that will fulfill the requirements. 

When selecting a material for acoustic treatment, particular con- 
sideration must be given to its absorption over the frequency spec- 
trum. It will be found, from both analyses and measurements, that 
the fixed absorption, or that provided by carpet, seats, drapes, etc., 
is generally high throughout the upper range, relative to its values 
at the lower frequencies. While smaller amounts of absorption are 
permissible at the lower frequencies, as will be observed from an 
analysis of Fig. 3, care must be taken to avoid introducing amounts 
of absorption appreciably below the desired limits at the low fre- 



394 



S. K. WOLF AND C. C. POTWIN 



[J. S. M. p. E. 



quencies or in excess of the requirements at the high frequencies. 
Fig. 4 shows the frequency-absorption characteristics of two typical 
acoustic materials having equal coefficients at 512 cps. The use of a 
large quantity of material B (Fig. 4) independently would result in 
extreme frequency distortion, causing a pronounced "boominess" 
at low frequencies and a most noticeable lack of brilliance at high 
frequencies. The increased average efficiency and more desirable 
characteristic of material A is particularly apparent, and may be 
regarded as falling well within the required limits for general theater 
use. Attention is called to the relative coefficients at 512 cps., and 



.90 
.SO 
70 
.60 
.50 

.20 

.10 


F 


~ 


















o 








/ 










1 








/ 


. 


!. 


"^^ 


- 


S 






s 

X/1 










H 

O 
T< . 




/ 


/ 















/ 




/ 












O 


r 


l 














P 




1 
I 






-Material A 

Material 6 




j 




7 
















m ^ 






frequency 


[ops. 








b 

IG. 4. 


* 128 256 512 102^- 20^-8 40< 
Comparative absorption char act 


b ffl92 
eristics. 



the importance of not considering this frequency only, when selecting 
acoustic materials for treatment. To approach an absorption 
characteristic approximating that obtained at the laboratory, the 
method of mounting the material for test should be carefully noted 
and followed accordingly when applying treatment. 

(2) Desirable Locations. The most desirable locations for the 
acoustic material are governed by the general shape of the theater 
and the relation of various surfaces to the sound-source. In theaters 
of satisfactory proportions, materials of high average absorption 
and favorable characteristics are most effectively placed upon the 
rear wall surfaces, particularly when these areas are of wide expanse 
and subject to considerable direct sound energy. The side walls, 



Oct., 1936] ACOUSTICAL DESIGN OF THEATERS 395 

extending forward from the rear wall, are generally the surfaces of 
next importance. The efficiency and extent of this further treatment 
for these areas are governed by the requirements of the particular 
theater under consideration. In theaters having balconies it is not 
generally necessary to treat the rear and side wall areas directly 
beneath the balconies unless the depth is less than approximately 
twice the height. When inefficient seats are used, a partial ceiling 
treatment of a material of moderate absorption and favorable char- 
acteristics is also desirable. 

CONCLUSIONS 

With due consideration to the fundamental requirements for acous- 
tical design and treatment, it is possible to plan a theater in which 
hearing conditions will meet with the full satisfaction and approval 
of the patronage. The general business outlook and anticipated re- 
venue from operation are largely dependent upon the quality and 
intelligibility of sound, since it has been determined from a careful 
survey that a large number of the theaters that fail financially are 
those that are noted for their undesirable acoustic conditions. 

It is believed possible to standardize, for definite reference, cer- 
tain of the data given above, in order that architects or engineers 
may be guided in solving the more common acoustic problems with 
which they are confronted. Our past experience in recommending 
the acoustical correction of more than 8000 theaters has indicated, 
however, that a large number of cases will arise in which standardized 
methods will not apply. In such cases and particularly those in- 
volving complete originality of design, reliable acoustic advice should 
be obtained before attempting the solution of problems that present 
any degree of complication. 

REFERENCES 

1 SABINE, W. C.: "Collected Papers on Acoustics," Harvard Univ. Press 
(1927). 

2 EYRING, C. F.: "Reverberation Time in 'Dead' Rooms," J. Acoust. Soc. 
Amer., I (Jan., 1930), No. 2, p. 217. 

8 SETTE, W. J.: "A New Reverberation Time Formula," /. Acoust. Soc. 
Amer., IV (Jan., 1933), No. 3, p. 193. 

4 KNUDSEN, V. O.: "The Effect of Humidity upon the Absorption of Sound 
in a Room, and a Determination of the Coefficients of Absorption of Sound in 
Air," /. Acoust. Soc. Amer., HI (July, 1931), No. 1, p. 126. 

* WATSON, F. R. : "Absorption Tests," American Seating Co. (1929) . 

6 Acoustical Materials Assoc., Chicago, 111. 



ANALYSIS OF SOUND WAVES* 
H. H. HALL** 



Summary. Most sounds consist of a spectrum of frequencies of various intensities. 
The distribution of the frequencies and intensities determines the quality of the sound. 
The spectrum may remain fairly constant in time, or it may go through rapid changes. 
Sound analysis is the process by which the various components of the spectrum are 
detected and measured. A complete analysis should furnish the frequency and ampli- 
tude of each component as well as its phase relatively to the other components, at a 
given instant of time. If the spectrum changes in time, a complete analysis should 
be made at intervals throughout the duration of the sound, the lengths of the intervals 
being determined by the rate at which the spectrum is changing. 

For purposes of analysis sounds may be grouped into four classes: (1) sounds 
that may be maintained at constant frequency, constant intensity, and unvarying 
quality for a period long enough to carry out the analysis; (2) sounds that are essen- 
tially transient in nature; (5) sounds that may be maintained constant, on the 
average, but whose frequency, intensity, and quality vary periodically within this 
time; (4) sounds that are entirely random inform but are continuously maintained. 
The first two groups of sounds require different methods of analysis. The third 
group in certain instances may be analyzed by the methods used for class 1, whereas 
in others the method used for class 2 may be necessary. Sounds of class 4 may 
be analyzed by all methods capable of analyzing sounds of class 1 with one 
exception. 

Instruments for analysis may be grouped into five classes: graphic, resonance, 
heterodyne, stroboscopic, and diffraction analyzers. The operation of each type of 
instrument is briefly discussed and the suitability of each for analyzing the various 
classes of sounds is brought out. Examples of analyses performed by the various 
methods are presented. 

It is well known that any wave may be represented by the sum of a 
series of sine waves of different frequencies whose amplitudes and 
relative phases are determined by the form of the original wave. 
Such a series of simple waves constitutes the spectrum of the wave, 
and, in the case of sound, the detection and measurement of the com- 
ponents of this spectrum are sound analysis. 

It follows that an ideal analysis must furnish the following data, 
referred to a specific instant in time : 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Cruft Laboratory, Harvard University, Cambridge, Mass. 
396 



ANALYSIS OF SOUND WAVES 397 

(1) The frequencies of all components. 

(2) The relative amplitudes of the components. 

(3) The relative phases of the components. 

If these data are known the original wave may be reproduced pre- 
cisely. The human ear, however, is not sensitive to phase, and a 
specification of the frequencies and amplitudes, therefore, is often 
sufficient. 

CLASSIFICATION OF SOUND WAVES 

Although musical sounds consist of a chain of nearly identical 
waves, other sounds are by no means of such nature. Even vowel 
sounds sung by a well trained voice exhibit more or less regular fluctua- 
tions of frequency, intensity, and wave-form while maintained on 
one note. In ordinary speech the frequency, intensity, and wave- 
form vary rapidly during the speaking of a single syllable, while in 
the case of noise such as the roar of heavy traffic or background noise 
in a sound-reproducing system, the waves are entirely random in form 
but have definite characteristics when averaged over a sufficiently 
long time. Other sounds of short duration, such as the slam of a door, 
may have definite characters but are completely transient in nature. 

From the point of view of analysis, sounds may be classified roughly 
into four groups : 

(1) Steady-state sounds, or sounds that may be maintained at constant 
fundamental frequency, constant intensity, and unvarying quality for periods 
long enough to carry out the analysis. 

(2) Sounds that are essentially transient in nature. 

(5) Sounds that may be maintained constant, on the average, but whose 
frequency, intensity, and wave-form are modulated at a constant frequency. 

(4) Noise, or sounds that are entirely random in form but which are continu- 
ously maintained. 

Regarded as spectra, the sounds of type 1 represent an array of com- 
ponents whose frequencies are integral multiples of the fundamental 
frequency, and whose amplitudes are determined by the character of 
the sound. Sounds of type 2 represent continuous spectra embracing 
all frequencies within wide limits. If the transient sound of this type 
endures for a fairly long time and varies but slowly, the distribution 
of amplitudes will be such as to emphasize frequencies in the neighbor- 
hood of those that would constitute the spectrum of the steady-state 
wave to which the transient wave is momentarily similar, and to sup- 
press the others. As the wave changes, the amplitude distribution 
changes accordingly. Sounds of type 3 are strictly steady-state 



398 H. H. HALL [j. s. M. p. E. 

waves, if the modulation frequency be taken as the fundamental. 
On the other hand, if this frequency is negligible with respect to that 
of the fundamental of the unmodulated wave, the wave may be re- 
garded as one whose frequency and form vary periodically. But the 
two representations of the wave are equivalent. The latter point of 
view, however, does not represent a complete resolution of the wave. 

METHODS OF ANALYSIS 

When the form of a given wave may be expressed as a mathemati- 
cal function or is available as a plot of displacement against time, the 




FIG. 1. The Henrici Analyzer. After the index stylus has been made to 
trace the curve, the amplitudes of the first five sine and cosine components 
may be read on the proper dials. A second tracing furnishes the next five, 
and so on up to fifteen pairs of components. ( Courtesy ofD. C. Miller. *) 

analysis may be made by direct computation. This is a laborious 
process, which may be avoided under proper conditions by employing 
instrumental methods. Instruments designed to accomplish it are 
based upon a number of different processes and may be classed as 
follows : 

(1) Graphic Analyzers. 

(2) Resonance Analyzers. 
(5) Heterodyne Analyzers. 

(4) Stroboscopic Analyzers. 

(5) Diffraction Analyzers. 



Oct., 1936] 



ANALYSIS OF SOUND WAVES 
GRAPHIC ANALYZERS 



399 



The graphic analyzer requires that the wave be recorded as a curve 
of displacement against time. The curve is enlarged to proper di- 
mensions and placed upon a horizontal board over which the analyzer 
may travel. A form of this instrument, the Henrici analyzer, shown 
in Fig. 1, has been described by Miller. 1 The stylus of the analyzer 
is made to trace the curve, and the frequencies and amplitudes of the 
components may be read on the proper dials. Amplitudes of sine 
and cosine series are given, which is equivalent to specifying the 
amplitudes and phases of a single series. In this way the first five 





FIG. 2. Freystedt's resonance analyzer. The switch connecting 
the filters to the measuring circuit and that connecting the hori- 
zontally deflecting plates of the cathode-ray tube to the battery are 
rotary, and are mounted upon the same shaft. The oscillator changes 
the whole frequency band by heterodyning to a more convenient 
range. (After E. Freystedt.*) 



components of the wave are given. Retracing the wave with a differ- 
ent setting of the instrument furnishes the next five, and so on up to 
fifteen components. 

The method assumes that the spectrum consists of components 
whose frequencies are integral multiples of that of the fundamental. 
This is true only for steady-state waves. The instrument, therefore, 
may not be used to analyze one wave taken from a rapidly varying 
transient sound. If the sound varies slowly enough, analyses may be 
made affording an approximation to the true spectrum that becomes 
better the slower the variation. 



400 



H. H. HALL 



[J. S. M. p. E. 



RESONANCE ANALYZERS 

Suppose the frequency range that it is desired to analyze be divided 
by small steps into a large number of frequencies, and that an array 
of vibrating reeds be provided, one tuned to resonance at each fre- 
quency. If a complex steady-state wave is applied to this assembly, 
the reeds whose frequencies are nearest those of components of the 
wave will be set into motion, and their amplitudes will depend upon 
the amplitudes of the components. Such an instrument 2 will furnish 
the frequencies and amplitudes of the components, but not their rela- 
tive phases. Other resonators may replace the reeds, such as elec- 



Open G string 



Open D string 




UL. 



Open G string, 
plucked at J /4 
of its length 



Open G string, 
plucked at l / 2 
of its length 



Open A string 



Open E string 



mi 



-* 



J.il 



i \nt-tnt I 



a on A string 



a on D string 



! M\ / ZV y '%& 1 

_ .^ t: wo_ j 

FIG. 3. Analyses of violin sounds made with Freystedt's analyzer. (Courtesy 
of Johann Ambrosius Barth.*) 

trical tuned circuits , tuned air chambers , 3 or band-pass filters . Fig . 2 
shows schematically an instrument of the last type, described by 
Freystedt. 4 There are in all twenty-two band-pass filters, three per 
octave, covering the range from 40 to 5500 cps. The outputs of the 
filters are connected one after another through a switching mechanism 
to the vertically deflecting plates of a cathode-ray tube. As the tube 
is switched from one output to another, the spot is moved a short 
distance horizontally, so that the pattern traced upon the screen of 



Oct., 1936] 



ANALYSIS OF SOUND WAVES 



401 



the tube is a series of vertical lines whose heights are proportional to 
the outputs of the niters and whose positions correspond to their fre- 
quencies. Fig. 3 shows some analyses made with this instrument. 
This form of analyzer is not subject to the arbitrary assumptions that 
apply to the graphic analyzer, because it responds to whatever fre- 
quencies are actually present in the wave, whether harmonic or not. 

If a periodic force is applied to a resonator at its frequency of reso- 
nance, it is well known that the amplitude of vibration of the resona- 
tor builds up gradually to a maximum at a rate that depends upon 
the damping. The increase of amplitude is rapid if the damping is 
large, and slow if the damping is small. An appreciable time is there- 
fore required to excite the resonators to full amplitude. On the other 
hand, if the resonator is to discriminate sharply between the reso- 
nance frequency and neighboring frequencies, the damping must be 
small. The designer of such an instrument must therefore choose 
between rapid response and resolving power. 



tw 

MICRO- 
PHONE 



AMPLIFIER 



BALANCED 
MODULATOR 



BAND PASS 
FILTER 



LOGARITHMIC 
VOLTMETER 



CAMERA 



OSCIL- 
LATOR 



CATHODE 
RAY TUBE 



FIG. 4. Diagram of heterodyne analyzer. 
HETERODYNE ANALYZERS 

The multiplicity of resonators of the resonance analyzer can be 
avoided by heterodyning. Referring to Fig. 4, the wave to be ana- 
lyzed and a wave whose frequency can be varied are applied to- 
gether to a detector or non-linear circuit element. The output of the 
detector will contain new components whose frequencies will be the 
differences between those of the applied wave and that of the variable 
wave. When the frequency of the latter is varied this group of com- 
ponents will vary with it. It is thus possible to require only one 
resonator or filter responding to a narrow band of frequencies, and to 
vary the frequencies of the difference-frequency band which, one by 
one, will actuate the resonator. This, in turn, operates a recording 
device. It may be shown that the amplitudes of these components 
are proportional to those in the original wave. This is often called 
the "search tone" method of analysis. Fig. 5 illustrates such an 
analyzer built by the author, 5 and Fig. 6 shows representative analyses 



402 



H. H. HALL 



[J. S. M. p. E. 



made with it. The amplitude of 
each component relative to the 
fundamental is measured upon 
the vertical scale. The response 
is logarithmic, and the range of 
amplitude is 60 decibels, or 1000 
to 1. The horizontal scale is 
frequency. The analyses are of 
the first eight cardinal vowels 
intoned by a male voice. Each 
peak indicates the presence of a 
component. The last example is 
an attempt to analyze the sound 
S, which is a sound of type 4, 
and is seen to consist of a 
continuous distribution of frequencies ranging from about 4500 to 
at least 10,000 cps. The fluctuations are low-frequency time varia- 




FIG. 5. The heterodyne analyzer 
built at the Cruft Laboratory. 



EECH SOUNDS 



1 *: I 

3 0-.-H 



FIG. 6. Analyses made by the Cruft Laboratory analyzer. The sounds are 
the first eight cardinal vowels intoned by a male voice. The sound S, in 
the last analysis, is seen to consist of a continuous distribution of frequencies 
of sufficient intensity to be important from about 4500 to at least 10,000 cps. 



Oct., 1936] 



ANALYSIS OF SOUND WAVES 



403 




tions of amplitude which cause the output of the analyzer to fluctuate 
as the analysis is made. An envelope covering the whole distribution 
is the only characteristic having a meaning in this case. 

It is at once clear that an analysis can not be made instantaneously 
by this method, because the resonator requires appreciable time in 
which to reach full amplitude of vibration after the wave has been ap- 
plied. This period, moreover, must elapse as many times as there 
are components to be measured. The method of analysis is there- 
fore slower than the resonance analyzer method, because the various 
resonators in the latter are excited simultaneously. It has the ad- 
vantage, however, of simpler construction and 
of being capable of indicating any frequency 
in a continuous range instead of a range 
divided into finite steps. The time required 
for the analysis, and, therefore, the time dur- 
ing which the wave may not depart appre- 
ciably from a steady state, may be shown to 
be proportional to the square of the resolving 
power of the instrument. Nevertheless, quite 
rapid analyses may be made with the hetero- 
dyne analyzer. The analyzer mentioned above 
will cover the range of 50 to 10,000 cps. in 
less than four seconds, and yet resolve compo- 
nents only 50 cycles apart, if they are of the 
same amplitude. Another instrument de- 
scribed by Schuck 6 makes analyses in about 
one-tenth of a second with a corresponding 
reduction in resolving power. 

STROBOSCOPIC ANALYZERS 

As described by de Nemes 4 a rotating disk may be used for wave 
analysis. The face of a disk is divided into concentric rings, as shown 
in Fig. 7, and each ring is divided into segments alternately black and 
white . The second ring from the center of the disk has twice as many 
segments as the first ring, the third three times as many, and so on. 
The disk is rotated at a constant speed fast enough to cause the seg- 
ments of the first ring to pass a given point at a frequency equal to 
the fundamental frequency of the wave to be analyzed. If the disk 
is illuminated by light whose intensity is varied to correspond to this 
wave, the rings corresponding to components present in the wave will 



FIG. 7. Strobo- 
scopic disk for analy- 
sis, designed to ana- 
lyze the first nine 
components of a 
steady-state wave 
when illuminated by 
light whose intensity 
is controlled by the 
wave to be analyzed. 
(From T. de Nemes? 
Courtesy of Julius 
Springer.) 



404 



H. H. HALL 



[J. S. M. P. E. 



appear to stand still. This assumes, of course, that the wave is in a 
steady state, and that only component frequencies that are integral 
multiples of the fundamental frequency are present. The variation 
of light intensity is accomplished by using a neon lamp modulated by 
an amplifier to which the wave to be analyzed is applied. The in- 




FIG. 8. Analyses made by the disk shown 
in Fig. 7. The rings that are entirely blurred 
show the absence of the corresponding compo- 
nents in the wave. Note the difference in 
phase between the fundamental and the next 
component, in the first example. (From T. de 
N ernes," 1 Courtesy of Julius Springer.) 



strument indicates phases very nicely, but the intensities of the com- 
ponents are not clearly given. Fig. 8 shows analyses of steady tones 
made in this way by de Nemes. The smallest ring, of which only a 
segment is shown in each case, corresponds to the fundamental. The 
presence of higher components is indicated wherever a ring appears to 
stand still. In the photographs the rings that are completely blurred 
represent components that are absent. 



Oct., 1936] ANALYSIS OF SOUND WAVES 405 

DIFFRACTION ANALYZERS 

There are two types of diffraction analyzers, one of which employs 
diffracted sound, and the other diffracted light. An example of the 
first type, described recently by Meyer, 8 makes use of a diffraction 
grating designed for sound-waves. Since the wavelength of audible 
sound may be several meters, and since the grating space must be 
comparable in width to one wavelength, it is necessary to change the 
wavelengths to more convenient values. This is done by heterodyn- 
ing by a fixed-frequency oscillator. In this case the heterodyne fre- 
quency is 45,000 cps., applied to a detector simultaneously with the 
wave to be analyzed. The resulting band of sum frequencies is am- 
plified and applied to a small ribbon loud speaker. The sound falls 
upon a concave grating made of steel rods, 3.4 mm. in diameter and 
spaced 3 mm. apart, as shown in Fig. 9. The rods are mounted in 



FIG. 9. Meyer's diffraction grating for sound. The elements are 
steel rods 3.4 mm. in diameter and 3 mm. apart. (From E. Meyer* 
Courtesy of J. A ecus. Soc. Amer.) 

two parallel iron plates 12 cm. apart, the whole grating being some 
three meters long. It has a theoretical resolving power of 125 cycles 
and a dispersion of 8 cm. per kilocycle. To observe the spectrum 
produced, a small condenser microphone is moved through the region 
in which the spectrum lies, and the output controls an oscillograph. 
Figs. 10 and 11 show analyses made in this way. 

The beauty of the method lies in the very short time required for 
the spectrum to be formed. This interval is the difference between 
the times required by the sound to travel from the nearest and far- 
thest grating apertures to the microphone. Meyer gives one 0.01 
second for this time. Theoretically, at least, it would be possible to 
observe the spectrum of a rapidly varying sound, which should ap- 
pear as a continuous spectrum. Unfortunately, this is difficult to 
carry out because there is nothing that is as sensitive to sound as the 
photographic plate is to light. Using the small microphone, however, 
a total analyzing time of approximately 0.1 second is obtained, 
which Meyer states is limited by photographic considerations. 



406 



H. H. HALL 



[J. S. M. P. E. 



1000 Hz 



2QOOHZ 



SOOOHz. 



Another ingenious diffraction analyzer makes use of diffracted 
light to produce the spectrum. Observation of the spectrum pro- 
duced by a diffraction grating may be used to study the form of the 
grating. Thus, when monochromatic light is used and the spectrum 
contains in addition to the single bright line a number of "ghosts," 
the imperfections of the grating may be computed from the positions 
and intensities of the ghosts. If a grating were made, the width of 
whose lines were varied in accordance with the wave-form to be ana- 
lyzed, then with monochromatic 
light a spectrum of ghosts would 
be produced that would be charac- 
teristic of the wave. This has 
been accomplished by Germansky 9 
in the following manner: The 
polished metal surface upon which 
the grating is to be made is 
covered with a thin coating of a 
mixture of glue, ammonium bi- 
chromate, and chromic acid, which 
has the property of becoming in- 
soluble in water when exposed to 
light. A variable-density photo- 
graph of the wave to be analyzed 
is prepared, and the treated metal 
surface is exposed to light that has 
passed through the variable-den- 
sity reproduction of the wave and 
a fine screen of alternately trans- 
parent and opaque parallel lines 
perpendicular to the axis of travel 
of the wave. After exposure, the unaffected coating of bichromate 
and glue is washed off, leaving a grating, the widths of whose lines 
vary in the desired way. The method is similar to that by which 
ordinary halftone plates are produced, except that a screen of paral- 
lel lines is used instead of a fine mesh. Such an analyzer has the ad- 
vantage that the spectrum may be recorded directly upon a photo- 
graphic plate. In the state in which it was described, the method 
can not compare with the sound diffraction analyzer ; yet, if there were 
some means of producing the grating simultaneously and continuously 
with the sound, the scheme would have a number of advantages. 




FIG. 10. Analyses of pure tones 
with Meyer's grating. (From E. 
Meyer* Courtesy of J. Acous. Soc. 
Amer.) 



Oct., 1936] 



ANALYSIS OF SOUND WAVES 
CLASSIFICATION OF ANALYZERS 



407 



Perhaps enough material has been given in this brief discussion to 
furnish a basis upon which the various types of analyzers may be 
classified. Such a classification is given in Table I. 

All types of analyzers are capable of analyzing sounds of class 1, 
or steady-state sounds. Sounds of class 2, or transient sounds, may 
strictly be analyzed only by diffraction analyzers. But if the tran- 



a 160.0. HZ 
1 2000 Hz 



, y 

JUwU 



Organ pipe 

850 Hz. 




FIG. 11. Analyses of various sounds made 
with Meyer's grating. (From E. Meyer, 8 
Courtesy of J. Acous. Soc. Amer.) 



sient sound varies slowly, the resonance and stroboscopic analyzers 
may be used. If the time of analysis is sufficiently short, the hetero- 
dyne analyzer may be used. If the variation of the transient is 
sufficiently slow, the graphic analyzer will give the steady-state spec- 
trum to which the sound approximates at any given instant. 

Any analyzer capable of analyzing a steady-state wave, provided it 
has sufficient resolving power, is effective in analyzing sounds of class 
3. If the frequency of modulation is negligible compared to that of 
the unmodulated fundamental, then it is permissible to use a graphic 
analyzer to analyze selected waves taken at different instants in the 
modulation cycle. But these analyses will be those of the steady- 



408 



H. H. HALL 



state wave to which the wave under investigation is instantaneously 
similar. 10 Sounds of class 4, which represent continuous spectra, can 
be analyzed by all analyzers, with the exception of the graphic and 
stroboscopic types. 



TABLE I 



Classification of Analyzers 



Type 


Input 


Time for Analysis 


Waves Analyzed 


Results 


Graphic 


Oscillogram 


1 hour 


Steady-state 


Frequency 








Slowly varying 


Amplitude 








Transient 


Phase 


Resonance 


Microphone 


0.1 second 


Steady-state 


Frequency 






Proportional to 


Slowly varying 


Amplitude 






resolving power 


Transient 




Heterodyne 


Microphone 


4 seconds 


Steady-state 


Frequency 






Proportional to 




Amplitude 






square of 










resolving power 






Stroboscopic 


Microphone 


0.05 second 


Steady-state 


Frequency 








Slowly varying 


Phase 








Transient 




Diffraction 


Microphone 


0.01 second 


Steady-state 


Frequency 








Transient 


Amplitude 



REFERENCES 

1 MILLER, D. C.: "The Science of Musical Sounds," MacMillan (New York, 
N. Y.), 1926. 

2 HICKMAN, C. N.: "An Acoustical Spectrometer," /. Acoust. Soc. Amer., 6 
(Oct., 1934), No. 2., p. 108. 

3 HEWLETT, C. W.: "Analysis of Complex Sound Waves," Phys. Rev., 35 (Nov., 
1912), No. 5, p. 359. 

4 FREYSTEDT, E.: "A Sound Frequency Spectrometer," Zeitschr. fur Tech. 
Phys., 16 (Dec., 1935), No. 12, p. 533. 

6 HALL, H. H.: "A Recording Analyzer for the Audible Frequency Range," 
J. Acoust. Soc. Amer., 7 (Oct., 1935), No. 2, p. 102. 

6 SCHUCK, O. H.: "The Sound Prism," Proc. I. R. E., 22 (Nov., 1934), No. 11, 
p. 1295. 

7 dE NEMES, T. : "Harmonic Analysis of Sound- Frequency Oscillations with a 
Stroboscopic Disk," Phil. Mag., 18 (Aug., 1934), No. 118, p. 303. 

dE NEMES, T.: "Instantaneous Frequency Analysis of Light Variations with 
Rotating Disks," Arch, fur Elektrotech., 26 (June, 1932), No. 6, p. 403. 

8 MEYER, E.: "A Method for Very Rapid Analysis of Sounds," J. Acoust. Soc. 
Amer., 7 (Oct., 1935), No. 2, p. 88. 

9 GERMANSKY, B.: "On an Optical Method of Fourier Analysis," Annal. der 
Physik, 7 (Nov., 1930), No. 4, p. 453. 

10 BARTHOLOMEW, W. T.: "A Physical Definition of Good Voice Quality in the 
Male Voice," /. Acoust. Soc. Amer., 6 (July, 1934), No. 1, p. 25. 



THE TECHNICAL BASIS OF X-RAY MOTION PICTURE 
PHOTOGRAPHY* 

R. JANKER** 

Summary. After considering the difficulties involved in the direct method of x-ray 
cinematography, in which the x-rays penetrate the subject and pass directly to the 
photographic film with intensities depending upon the absorption of the subject, 
some of the work done by the author by means of the indirect method is described. 
In the indirect method, the x-ray image of the subject upon the fluorescent screen is 
photographed in reduced size by means of a suitable lens system. Various difficulties 
and factors of the system to be considered are discussed, and examples of the results 
attained by the indirect method are presented. 

The desire to render visible the activities of the internal organs 
by means of x-ray motion pictures is almost as old as the knowledge 
of x-rays themselves. A method of doing so was first proposed in the 
year in which Rontgen published his discovery, but only recently has 
it actually become practicable. Technical difficulties have been re- 
sponsible for the failure of the accomplishment to catch up with 
the desire. 

When we wish to record and reproduce movement in a picture we 
divide it into 16 to 18 separate phases per second. Upon projection, 
the human eye can no longer separate the individual pictures as 
rapidly as that, so we have the impression of motion. 

Now let us consider how an x-ray picture is produced. Rays emitted 
from an x-ray tube penetrate the object, and, depending upon the 
thickness and composition of the object, undergo more or less weaken- 
ing by absorption. Proceeding in straight lines, the rays strike the 
photographic emulsion and produce an image of the object by virtue 
of their differing intensities. The size of the image corresponds closely 
to that of the object; but actually, because the rays are projected from 
a small source, the image is somewhat larger than the object. If, for 
example, it were desired to photograph the human thorax by means of 
x-rays, it would be necessary to use a film 30 cm. long and 40 cm. 
wide. Since 16 to 18 pictures per second are required, in one second 

*Presented at the Spring, 1936, Meeting, Chicago, 111. 
**University of Bonn, Bonn, Germany. 

409 



410 R. JANKER [j. s. M. p. E. 

16 to 18 times an area of 30 X 40 cm. of film would be used; i. e., a strip 
of film 40 cm. wide and from 4.8 to 5.4 meters long per second. Con- 
struction of a projector in these proportions is out of the question, and 
for projection in existing apparatus, the image must be reduced to nor- 
mal size. It does not need to be emphasized that the cost of the ma- 
terials in the large size would be prohibitive. 

In this so-called direct method (Fig. 1) there are still other appreci- 
able technical difficulties. The film band must be moved intermit- 
tently 16 to 18 times per second through the length of a frame (30 
cm.), and must be stopped and exposed during each stationary period. 
Furthermore, it would be necessary to abandon the use of intensifying 
screens; a thing that could not be tolerated for such short exposures, 
since the fluorescence augments the photographic effect of the x-rays 
considerably. These screens would have to be pressed flat against the 
film by means of plates, and both plates and screens carried along 
together by the film; or they would have to be raised from the film 
from 16 to 18 times per second while the film is moved, and then 
pressed against the film during each exposure period. Difficult 
problems of construction would be created by the necessity of moving 
such large amounts of material back and forth. A number of at- 
tempts have been made to solve this problem. It was necessary to 
restrict the pictures to small objects, and, therefore, to small film 
sizes, such as I usea in photographing guinea pigs and similar animals 
at 22 frames per second, or else to photograph large objects over such 
very short intervals of time that the process can not really be spoken 
of as motion picture photography. 

Another method gives much better results: indirect x-ray motion 
picture photography (Fig. 2) . The x-ray image on a fluorescent screen 
is photographed in reduced size by means of a suitable lens system. 
In this method an entirely new difficulty arises. When it is considered 
how much illumination is required for taking pictures in the studio, 
it is readily understood that the brightness of the ordinary fluorescent 
screen is quite inadequate for instantaneous exposures. It should be 
remembered that the physician who wishes to view such a fluorescent 
image has to become adapted to the dark for at least a minute. Even 
with the greatest intensity attainable with modern x-ray apparatus, 
the screen brightness is much too low. In my first experiments in 
1926, in spite of 10 seconds' exposure for each photograph, the results 
were not satisfactory. Therefore, in order to obtain 16 to 18 pic- 
tures per second, not only must the fluorescent screen operate under 



Oct., 1936] X-RAY MOTION PICTURE PHOTOGRAPHY 



411 




FIG. 1. Schematic arrangement for direct x-ray cinematography; R, 
x-ray tube; Ob, object; F, film. 




FIG. 2. Schematic arrangement for indirect x-ray cinematography : R, 
x-ray tube; O bt object; L, fluorescent screen with image O p> motion pic- 
ture camera. 



412 



R. J ANKER 



[J. S. M. P. E. 



optimal conditions, but other features of the method must be greatly 
improved. The following factors are to be considered : 

(1) X-ray apparatus 

(2} X-ray tube 

(5) Fluorescent screen 

(4) Lens system 

(5) Motion picture camera 

(6) Film 

With systematic work over several years, considerable progress 
has been made. It is possible in this paper to refer only briePy to the 
various points. 

(1) At first, ordinary commercial x-ray apparatus was used; how- 




FIG. 3. Zeiss//0.85 lens, on Askania x-ray camera. 



ever, the power was too low for the purpose, chiefly because the equip- 
ment did not produce the necessary current intensities at high 
potentials. Finally, a suitable x-ray generator with a supplementary 
condenser was built. Its details will not be discussed here. 

(2) The available x-ray tubes did not fulfill the requirements. 
Thanks to the aid of the firm of Siemens, we now have tubes with 
revolving anodes, which, in spite of the greatly increased power load, 
have a relatively small focal spot capable of producing sharp definition 
in the x-ray image. 

(3) To obtain the best available fluorescent screen, samples of 
both domestic and foreign manufacture were tested. First of all, 



Oct., 1936] X-RAY MOTION PICTURE PHOTOGRAPHY 413 

on account of the variations in spectral quality of the fluorescent 
light, each screen had to be tested with films of various sensitivities 
in order to find the most satisfactory combination. At the present 
time we are using a special make of Heyden and Siemens screen. 

(4) Particular trouble was encountered in producing a lens of 
sufficiently high aperture. Considerable progress was made with a 
Zeiss Biotarf/lA lens, although we were not satisfied with it or with 
an //l.O lens that the Ruo Werke succeeded in making. We hope 
that the lens in use at present, the Zeiss //0.85, for substandard and 
standard films (focal length 5.0 or 12.0 cm.) does not represent the 
final improvement from the German optical industry. 

(5) The motion picture camera was so designed that with a 
constant picture frequency the pull-down time was made as short 
as possible in order to lengthen the exposure time of the individual 




FIG. 4. Askania camera with drive for various speeds and time-lapse 
attachment. 



pictures. During the earlier years we worked to the extreme limits 
of this principle, with a camera we constructed ourselves, having no 
shutter and a pull-down speed not reached heretofore. Now we 
use a camera built by the Askania Works according to the author's 
specifications, in which the time is not shortened nearly so much 
(270-degree light sector, 90-degree dark sector) (Figs. 3 and 4). 

(6) At first, the best films obtainable were not nearly sensitive 
enough for x-ray motion picture photography. We therefore at- 
tempted to sensitize the films ourselves, but because of the difficulties 
involved we no longer do so. We now use the commercial materials, 
Kodak P anatomic film and Agfa Pankine H film. 

Through the continued improvement of these factors it has been 
possible to produce a large number of experimental films of animal 
subjects and a number of films of human beings (Fig. 5) . The quality 
of the pictures became improved with experience, particularly by 



414 R. JANKER [j. s. M. p. E. 

increasing the distance between the x-ray tube and the object. 
This was kept as small as possible at first, with the aid of insulating 
layers between the patient and the (high-tension) tube, in order to 
attain a sufficient x-ray intensity (which decreases as the square of 
the distance). Associated with this short distance was some degree 




() (b) (c) (d) 

FIG. 5. Examples of x-ray cinematography: 
(a) Bronchial tree of cat, after injection of contrast solution. 
(&) Injection of contrast solution into pericardium of cat. 

(c) Movement of elbow joint in myositis ossificaus. 

(d) Human heart and lungs. 

of haziness of the image. Now we can work at distances great enough 
to afford satisfactory image quality. 

During the course of the year, partially through the support of the 
German Science Notgemeinschaft and of a group of friends and 
promotors at the University of Bonn, it was possible to make many 
improvements and develop more extensive facilities for x-ray motion 
pictures. Too much space would be required to describe* all these 
details. Two pictures with brief comments (Figs. 6 and 7) are in- 
cluded here, of those made so far. 

There is still another difficulty that has not been mentioned: the 



Oct., 1936] 



X-RAY MOTION PICTURE PHOTOGRAPHY 



415 





416 R. JANKER [j. s. M. p. E. 

danger of higher and higher x-ray dosages to the subject. Man can 
tolerate only a certain quantity of x-rays. If this amount is exceeded 
then more or less serious changes in the skin and the internal organs 
occur. It is only necessary to mention that these changes are prac- 
tically irreparable and incur the risk of cancer later. 

On this account no exposures are given that can harm the patient 
in any way. The limit of permissible radiation is reached in 50 
seconds of motion pictures. Actually, however, one should keep well 
below this limit so that in no case will the exposures exceed 15 or, at 
the most, 20 seconds. For that reason, the next step in x-ray cine- 
matography should be a further reduction of the intensity required, 
so that this method, using the longest possible lengths of film, can 
be added to the present roentgenological methods without endanger- 
ing the patient. In this way, the procedure should offer a very im- 
portant advancement in diagnosis. 

It will be obvious that we have made use of other developments in 
technic, such as time -lapse and high-speed studies. Naturally, 
special apparatus was required. In time-lapse work (for example, 
one frame per second, with projection at normal speed) arrange- 
ments have to be made to expose a picture every two seconds. By 
means of commutators coupled to the camera, the x-ray apparatus is 
made to operate intermittently. In this way it is possible to record 
movements such as intestinal action extending over a period of some 
hours, and to reproduce the characteristic movements by projection 
at normal speed. On the other hand, with the high-speed camera, 
by photographing at a greater-than-normal number of frames per 
second and projecting at the normal rate, very rapid movements such 
as the contractions of the heart, which are difficult to analyze because 
of their rapidity, can be studied in detail. As early as 1932 we were 
able to take 100 pictures per second of a rabbit's heart. Unfortunately, 
at present we do not have a high-speed camera available; otherwise, 
we should be able to work at 200 or 300 pictures per second. With 
our present Askania camera we have already photographed the human 
heart at 50 frames per second. The camera is not mechanically suit- 
able for greater speeds ; otherwise, we should certainly have done work 
at higher speeds. 

The problems of x-ray motion picture photography are not yet 
exhausted. Sound and picture can be recorded simultaneously; for 
example, the movement of the soft palate, epiglottis, and larnyx 
can be taken simultaneously with speech. 



Oct., 1936] X-RAY MOTION PICTURE PHOTOGRAPHY 417 

By way of special scientific experiments, the passage of the blood- 
stream can be followed with x-ray photographs. X-ray motion 
picture photography has become a scientifically exact and useful 
method of investigation. The films of animal experimentation and 
of human beings obtained by the Reichsstelle fur den Unterrichtsfilm 
show briefly what it is possible to do as a means of instruction. 

(At the conclusion of the paper a short 16-mm. x-ray sound motion picture was 
shown. It included several examples of the vocal organs of males and females. De- 
tails of tongue and other fleshly portions of the head were shown clearly as well as the 
bone structure.) 

NOTE 

The scientific work described in the foregoing article was carried out by Prof. 
Janker of the Chirurgische Institut of the University of Bonn and supported by 
the "Reichsstelle fur den Unterrichtsfilm, Gemeinnutzig G. m. b. H." 

The Reichsstelle fur den Unterrichtsfilm is an official body, supported by the 
German Government. One of its main tasks is to supply educational and scientific 
films for use in all types of German schools, including elementary schools, high 
schools, and universities. The schools are obliged to purchase their taking appara- 
tus and projectors through this body, which will then assist them with their 
advice. The Reichsstelle fur den Unterrichtsfilm is connected with technical 
departments at the technical high school of Berlin-Charlottenburg which deal 
with standardization questions concerning apparatus and films for the above- 
mentioned purpose. 

From the establishment of the Reichsstelle fur den Unterrichtsfilm in 1934, to 
February 28, 1936, 7037 16-mm. equipments have been delivered to German 
schools and 29,985 prints having an aggregate total length of 3,598,200 meters of 
16-mm. film ha\e been released for school purposes. This body also supports the 
scientific work of the German universities and technical high schools, of which 
the foregoing paper is an example. 

The official journal of this institution is Film und Bild, in part 2 of which (1936) 
this paper was first published. 

DISCUSSION 

MR. CRABTREE : I have been wondering whether the doses used to obtain these 
pictures were fatal or not. 

MR. AUTEN: Suitable x-ray dosages are not dangerous to the patient. The 
dosage can be so regulated that exposures up to thirty minutes are quite safe. 
Of course, it is rather dangerous to the physician because he spends his whole 
lifetime in the work, but not to the patient. 

MR. TOENNIES: Physicians are always very careful to shield themselves against 
the x-rays. The doses given to the patients are near the danger point. X-ray 
cinematography is always very dangerous, because the intensity necessary for 
the time of shooting is much greater than that required for an ordinary still pic- 
ture. Damage done by excessive doses can appear after a couple of years, in the 
form of cancer, for which at this time no cure is known. Injury is possible also 
when no skin burning has occurred. Young persons are in greater danger than 



418 R. JANKER 

older ones. No motion picture engineer should work in this field without the 
advice of an x-ray expert. 

MR. ROBERTS: Referring to the method described in the paper, the voltage 
on the tube is so great that probably many of the x-rays will pass through the 
screen. I wonder whether any trouble was experienced with the rays getting 
into the camera, upon the film, and perhaps into the lens. 

MR. MORTON: The back of the fluorescent screen is covered with a heavy 
sheet of lead glass which prevents the x-rays from reaching the camera. 

MR. TUTTLE: Guinea pigs used in our work have died from burns after five 
minutes of continuous exposure. They do not die immediately, but within a 
week or so. Of course, the x-ray tubes are tremendously overloaded to get the 
exposures we want: about 300 ma., 80 kv., at 14 inches. We have not subjected 
human patients to x-rays for longer than two minutes over a period of two or three 
months, and only for short exposures about 35 seconds each time. 

To keep the x-rays out of the camera, we built a special lead shield with a socket 
that fits right around the lens, so the camera is virtually shielded from x-rays. We 
also used a lead glass in conjunction with the intensifying screen. 

MR. WOLF: Does the person exposed to x-rays recover completely after in- 
termittent exposure, or is there always some damage done by exposure? 

MR. TUTTLE : I can not answer the question conclusively. I know that, in the 
case of doctors and technicians who have spent a long time at the work, and are 
affected only slightly, getting completely away from x-rays for six months seems 
to restore their health. I do not know anything about the time of recovery or the 
possibility of recovery if they are actually burned. Slight burns cause loss of 
hair and a redness of the skin that may never entirely heal. Long exposures or 
serious burns affect the bone marrow. With this kind of burn a person may live 
three or four years. Much depends upon their general health and other factors. 
In any case, it is extremely dangerous to use x-rays on human subjects, and they 
should not be used without medical advice. 



A FILM EMULSION FOR MAKING DIRECT DUPLICATES 
IN A SINGLE STEP* 



W. BARTH** 

Summary. Duplicates of positives or negatives can be made by the familiar 
process of exposure, standard development, and fixation of a single film without 
requiring second exposure and development, as in the case of amateur motion picture 
reversible film, or resort to the duplicate negative process. Contact printing is re- 
quired with exposures about equal to those used in printing chloride photographic 
paper emulsions. The emulsion, although of silver bromide composition, is of a 
type entirely different from all other photographic emulsions, making use of the 
solarization effect for the first time in practical photography. Some commercial 
possibilities of the new type of emulsion are seen in the duplication of x-ray and 
other valuable transparency originals, aerial mapping, motion picture still picture 
printing, photo reproduction practice, and general commercial photography. 

This paper, although concerned in one respect with motion picture 
film only as used for miniature photography, is submitted because 
it deals with the practical photographic use of the phenomenon of 
solarization. The process is new, interesting, even surprising, and 
it is felt that it holds great promise in respect to simplifying greatly 
the photographic process in general. 

Let us start with the characteristic density-log exposure curve as 
shown in Fig. 1 for an ordinary photographic silver halide emulsion 
normally exposed in a sensitometer and developed in some common 
photographic developer, such as metol-hydroquinone-sodium car- 
bonate and fixed in regular hypo. Only the parts A, B, and C, 
known respectively as the toe, straight-line portion, and shoulder 
of the curve, have been of practical importance for the regular nega- 
tive, positive, or reversible emulsion; while the portions M and 
especially S are undesirable in any emulsion, because the registration 
of the light values in this part of the characteristic curve is distorted. 
The emulsion of the direct duplicating film now makes practical use 
of the part S, or the solarization portion of the characteristic curve. 
The effect here of exposure is exactly the reverse of the effect in the 

*Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Agfa Ansco Corp., Binghamton, N. Y. 

419 



420 



W. EARTH 



[J. S. M. P. E. 



A, B, C portion. Before the maximum density M is reached, the 
density of the developed silver image increases with increase of 
exposure. Within the solarization range the density decreases with 
increase of exposure, or, in other words, a print, made from an original 
negative using only the solarization region, will be a negative, and a 
print from an original positive will be a positive in either case, 
therefore, a duplicate of the original. Fig. 2 shows practical results 
attained 1 with an emulsion of this kind. For the left-hand picture 
an ordinary negative film was exposed in the camera; for the right, 
the direct duplicating film. The difference in exposure is indicated 
beneath the illustrations. The pictures were developed together in 
the same developer and fixed together in the same fixer. Applying 



Log I 



FIG. 1. Characteristic curve taken from the time-intensity- 
density surface of the extra-rapid plate. 1 



the same technic we get in one case the usual negative, in the other 
a duplicate. This duplicate is the exact replica of the original 
obtained in a single step, namely, a negative from a negative and a 
positive from a positive, as differing from the ordinary methods, 
which reverse the character by turning a negative into a positive or 
a positive into a negative. 

There are other processes in photography that transfer the detail 
of a subject or picture to a film without reversing its light and shade 
values or, in other words, which produce a duplicate in a single step. 
Two may be mentioned here which do not employ a silver bromide 
emulsion. Bichromate gelatin is sensitive to light and is hardened 
by exposure. When the resulting gelatin relief obtained after the 
exposure is treated with a dye solution, the unexposed parts are 
colored, while the exposed parts, because of the hardening effect 



Oct., 1936] FILM EMULSION FOR DIRECT DUPLICATES 421 

during the exposure, remain colorless, and thus a duplicate dye 
picture is obtained. 

Certain diazo compounds when struck by light are decomposed 
and become incapable of forming an azo dye. Unexposed parts of a 
diazo paper (such as Ozalide) when treated with ammonia, form a 
dye, i. e., a density, while the exposed parts remain clear. The 
result is likewise a duplicate of the original. 

Then there is the commonly known chemical reversal process used 
for processing amateur motion picture film. The emulsion is of 
about the same type as the ordinary positive or negative emulsion, 
and the toe, straight-line porti'on, and shoulder of the sensitometric 




Super-plane-filmpack Direct duplicating film 

(//ll; 1/50 sec.) (//4.5; 10 sec.) 

3!/2 min. Rollfilm developer 3 min. 

FIG. 2. A negative at the right, a positive at the left, although the two films, 
after being exposed in the camera, have been developed and fixed together in the 
same solutions. 

curve are the essential parts here as in the regular positive and 
negative film developing process. The reversal effect is produced 
in this case by a bleach, second exposure, and second development, 
all after the original or first development. 

The principle used in the direct duplicating film fortunately differs 
from all these. On account of its being a silver halide emulsion, the 
resulting picture is a silver image ; but, unlike the reversible emulsion, 
it can be exposed, developed, and fixed similarly to all familiar photo- 
graphic materials of silver halide type. 

There are occasions in practical photography when, by accident, 
a partial duplicate results from very great overexposure of an ordi- 
nary emulsion. To produce the solarization effect intentionally, 
one would have to choose the emulsion carefully because there are 



422 



W. EARTH 



[J. S. M. P. E. 



great differences in solarization. Some emulsions show greater 
susceptibility to solarization, and some show hardly any. Further, 
one would have to expose the emulsion up to the point M (Fig. 1) of 
maximum density, a procedure that is not very practicable. But 
in almost all cases it turns out that the characteristic curve is not 
sufficient for practical use, because the film does not show sufficient 
clearness and also because the density range of the solarization is 
not sufficient. All these difficulties have been overcome by the 
direct duplicating film. No preliminary exposure is necessary, but, 





/ 


-^ 






f 


/ 


/ 


V- 




CINE 


/POSITIVE 


/ 


DIRECT\ DUPLICAT 


NG 


/ 




CONVIRA/PAPER 


\ 




_x 




/Log 1 


^ 


s^ 



FIG. 3. 



2.0 3.0 

Characteristic curves: 



Film 

Positive 35-mm. 
Convira paper 
Direct duplicating 



Development Time 
4 min. 
2 



Developer 

Positive 

Paper 

Direct duplicating 



so to speak, has been included in making the emulsion. Further- 
more, the photographic qualities of clearness, gradation, etc., are 
such that the direct duplicating emulsion is of real practical value. 

The method of making this emulsion 2 is based upon the idea of 
replacing a preliminary exposure by a special ripening process. In 
the first place, a normal photographic emulsion having a very pro- 
nounced solarization is chosen. The emulsion is brought up to the 
point M, where the solarization range S begins, not by preliminary 
exposure, but by a special ripening in the presence of substances 
that cause fog. For instance, with an addition of silver nitrate or 
of photographic ripening substances, or of developing agents such 
as hydroquinone, the emulsion is treated at a high temperature for 



Oct., 1936] FILM EMULSION FOR DIRECT DUPLICATES 423 

a certain length of time. Later the surplus of the fog-producing 
agents is washed out. Not all emulsions give the same good result, 
but it can be said that all emulsions that show suitable solarization 
show at least a good solarization curve when ripened in the presence 
of fog-causing agents. 

Fig. 3 shows the sensitometric curve of the solarized emulsion 
made in the manner described and used for the direct duplicating 
film. Of course, to achieve this result the original emulsion must 

TABLE I 

Some Data on Direct Duplicating Film with Various Developers 

Development 

Time Density Gamma Latitude 2 n 

Developer (Minutes) Max. Min. n 

Direct duplicating 4 

6 
8 

X-ray 3 l / t 

5 
8 

Glycin 8 

12 2.4 0.15 -1.7 6.5 

20 

Borax fine-grain 8 

12 1.6 0.12 -0.8 7.5 

20 

Amidol 4 

6 2.2 0.20 -1.7 6 5 

10 

show pronounced solarization, and the most favorable conditions 
for the special ripening process must be determined experimentally. 
The range of density of the emulsion used in making the direct 
duplicating film is greater than 2.0 under suitable development, 
with a maximum density of about 2.5 and a minimum density (fog) 
of 0.1. The range of exposure covered by this curve is ample to 
produce photographically valuable results. 

From Fig. 3 it can be seen that the general speed of the direct 
duplicating film is slightly less than that of the average contact 
printing paper. The speed is considerably less than that of motion 
picture positive film, a fact that makes the direct duplicating film 



1.9 


0.06 


-1.5 


2.5 


0.08 


-2.3 


2.7 


0.10 


-2.7 


2.2 


0.08 


-2.0 


2.6 


0.10 


-2.5 


2.7 


0.12 


-3.0 


1.8 


0.12 


-1.3 


2.4 


0.15 


-1.7 


2.7 


0.25 Y 


-2.2 


1.1 


0.10 


-0.6 


1.6 


0.12 


-0.8 


2.0 


0.18 


-1.1 


1.5 


0.15 


-1.3 


2.2 


0.20 


-1.7 


2.4 


0.25 Y 


-2.0 



424 



W. EARTH 



[J. S. M. p. E. 



not quite suitable as yet for duplicating purposes in the motion 
picture industry. 

Considerable experimenting has been done with various developers 
for the direct duplicating film. Table I shows some of the more 



TABLE II 

Developers Listed in Table I 

Developer Composition 

Direct duplicating Metol 

Sodium sulfite (anhydrous) 

Hydroquinone 

Sodium carbonate (mono) 

Potassium bromide 

Water 



5 grams 
35 grams 

3 grams 
grams 
gram 
cc. 



30 

1 

1000 



(To be diluted with 1 part of water; development time, 6 minutes at 65) 



X-ray 



Glycin 



Borax fine-grain 



Amidol 



A metol-hydroquinone-sodium 
carbonate developer with 

Metol 3 . 5 grams 

Hydroquinone 9 . grams 

Water 1000 cc. 

Glycin 50 grams 

Sodium sulfite (anhydrous) 125 grams 

Potassium carbonate 250 grams 

Water 5000 cc. 

Metol 1 . 5 grams 

Sodium sulfite (anhydrous) 80 . grams 

Hydroquinone 3 . grams 

Borax 3 . grams 

Potassium bromide . 5 gram 

Water 1000 cc. 

Amidol 20 grams 

Sodium sulfite (anhydrous) 100 grams 

Water 5000 cc. 



important results, while Table II describes the developers used to 
attain them. 

As indicated by the maximum densities listed in Table I, the 
metol-hydroquinone-carbonate developers, such as direct duplicating 
or x-ray film developer, give densities higher than 2.5 in normal de- 
veloping time. The glycin developer also reaches densities of 2.5, 
although the rather long development time required appears to be 
an inconvenience for practical use. Soft working developers, like 



Oct., 1936] 



FILM EMULSION FOR DIRECT DUPLICATES 



425 



the borax fine-grain developer, give a lower maximum density. Their 
advantage lies in the natter gradation and in the longer scale. Amidol 
developer renders a maximum density of 2.5, which is remarkable 
when it is considered that this developer contains no alkali. 

All developers produce an increase in fog with an increase in de- 
velopment time, but metol-hydroquinone-carbonate developers give 
the best clearness with a fog of 0.08 to 0.12. Slower developers 
show a higher fog; for instance, the borax developer produces a fog 
of almost 0.2 before a density of 2.0 is attained, while the more rapid 
developers give maximum density before this fog value is reached. 



3.0 



1.0 




4mltv 



Log 1 



FIG. 4. Characteristic curves of direct duplicating film, de- 
veloped in direct duplicating film developer for 4, 6, and 8 
minutes at 65. 



In regard to the increase of fog with increased development time, 
the exposed silver halide grain of the direct duplicating film acts in 
the same way as the unexposed grain of the ordinary emulsion. 
However, in the case of the direct duplicating film the higher fog is 
sometimes accompanied by a slight yellow stain, as indicated by Y 
in Table I. 

The gradation changes with the development time in the same 
manner as for ordinary film. Fig. 4 shows the increase of gamma 
as the development time is increased from 4 to 8 minutes. 

All gamma values are indicated as minus, following the geometrical 
definition of gamma as the tangent of the angle between the straight- 
line portion of the curve and the abscissa. So this distinction is 



426 



W. EARTH 



[J. S. M. p. E. 



made between positive gamma, indicating increasing density with 
increasing exposure, and negative gamma, indicating decreasing 
density with increasing exposure. 

The gamma value of about 2.0 to 2.5 for normal development 
time indicates that the direct duplicating film emulsion has a contrast 
nearly the same as that of motion picture positive film (see Fig. 3). 




FIG. 5. Sensitometric curves of direct duplicating film for 
various developers: 



Developer 
X-ray 

Direct duplicating 
Glycin 
Borax 



Minutes 
5 
6 

12 
20 



The curve for amidol developer, 8 minutes, is practically 
identical to the curve for glycin, except for the higher fog 
of 0.2, instead of 0.15 for glycin. 

With the borax fine-grain developer, however, a gamma as low as 
1.0 may be obtained (Table I). 

In Fig. 5 the sensi tome trie curves of various developers are shown. 
The threshold speed, indicated at T, is the same for all developers. 
There are considerable differences in the gradation, such as 1.1 
for borax developer and 3.1 for x-ray developer. The ranges of 
exposure, registered by differences in density, differ as indicated by 
the distances along the abscissa from points T to points 0. For 
the borax developer, this range is about 2 7 5 , whereas for x-ray 
developer it is only 2 6 . These illustrations show that the direct 
duplicating emulsion has characteristics similar to those of the 



Oct., 1936] 



FILM EMULSION FOR DIRECT DUPLICATES 



427 



normal types of emulsion: for instance, increase of gamma and fog 
with increasing development time. 

Besides these facts, which are of practical value, there are other 
properties of the emulsion that are more or less of theoretical value, 
two of which may be mentioned here. It is known that silver bromide 
emulsion, when immersed in a solution of methylene blue before 
development, shows quite an increase in fog. The same effect takes 
place with direct duplicating film (see Fig. 6). The maximum 
density in this case is only slightly less, while the fog increases con- 
siderably. Also the gradation becomes flatter. 





Lag K 



FIG. 6. Influence of methylene blue treatment: (B) film 
immersed in solutipn of 0.01 per cent methylene blue in water, 
and developed in x-ray developer; (A) film not treated with 
methylene blue solution. 

Another interesting fact is the influence of physical development 
upon direct duplicating film (fixation before development). It is 
known that most ordinary photographic emulsions can be developed 
by physical development. The picture thus obtained is of the same 
type as the picture obtained after chemical development, but the 
range of density is much less and a physically developed picture 
generally has considerable fog. 

Direct duplicating film was treated after fixation by physical 
development in the following way: The same negative was printed 
upon two sheets of direct duplicating film, the exposure being the 
same for both. One sheet was developed chemically in direct dupli- 
cating developer; the other, directly after fixing the exposure, in a 



428 W. EARTH [j. s. M. P. E. 

20 per cent sodium thiosulfite solution. The latter was washed very 
carefully, dried, and subsequently developed in a paraphenylene 
diamine silver nitrate developer recommended by Lumiere and 
Seyewetz. 3 The development time was 20 to 40 minutes. After 
final washing and drying, the result was the positive shown in Fig. 7. 
The density range of this positive is about 0.7, with a fog of about 
0.4 and a maximum density of about 1.1. 

The result is remarkable in two respects: The exposure was the 
same for both the physically and the chemically developed films; 
the chemically developed film is a duplicate. The physically de- 
veloped film is a negative of the original. 

The surprising results achieved with this film might be discussed 
as they relate to various photographic theories. However, as the 
work is still in the experimental stage, and as new, interesting, and 
more complete results are expected to follow, it would be inopportune 
to go into such details at this time. 

From the standpoint of further expansion of photographic theory 
it can be seen that the direct duplicating emulsion has great interest 
and promise. But the film is expected to find a place also in the 
field of practical photography. In general, the direct duplicating 
film can be used when duplicates are to be made of still pictures; 
for example, for making duplicates of portraits, commercial pictures, 
x-rays,* and in aerial photography. Making such duplicates re- 
quires only a single step and the film is handled just as is contact 
printing paper. 

Another field projected for the direct duplicating film is in minia- 
ture photography, as has been pointed out by Rahts. 4 Miniature 
camera users have often regretted the difficulty of retouching their 
negatives, which can be accomplished only by making enlarged 
positives from which is made the contact negative for retouching. 
This lengthy double-step procedure is often detrimental to the 
pictures. 

The reversible Leica film was introduced to help solve this problem 
as, instead of negatives, the user had a miniature positive which 
could be enlarged directly to a negative in one step. However, 
the disadvantage encountered in the use of such film is that, once 
used, two steps are required for every positive enlargement. By 

* The direct duplicating film is now available for making duplicates of x-ray 
originals. It is coated upon the same blue-tinted base as used at present for 
normal x-ray film. 



Oct., 1936] FILM EMULSION FOR DIRECT DUPLICATES 



429 




FIG. 7. Two films exposed for the same time under the same 
x-ray negative: (Left) film developed in direct duplicating de- 
veloper and then fixed, resulting in a duplicate; (right) film, after 
same exposure, fixed and then developed in a physical developer, 
resulting in a negative. 




FIG. 8. Direct duplicating film in miniature photography: (Left) un- 
retouched enlargement; (right) enlarged positive obtained from enlarged 
partially retouched negative made in a single step with direct duplicating 
film. 



430 W. EARTH 

using direct duplicating film with miniature negatives, only shots 
that need retouching require the double-step positive. 

Here the direct duplicating film proves very useful. It provides 
the possibility of making from every original miniature negative 
an enlarged duplicate negative which may be used for retouching. 
The miniature negative is placed in the enlarger with the emulsion 
side facing the lamp. The emulsion side of the direct duplicating 
film faces the miniature negative. In this way the relative positions 
of the left and right sides are reproduced as in the original. The 
photographic characteristics of the direct duplicating film are flexible 
enough as to gradation to provide a satisfactory enlarged negative, 
and from this a satisfactory enlarged print. Fig. 8 shows one print 
made directly from the miniature original, compared with another 
print made from an enlarged negative on direct duplicating film. 

REFERENCES 

1 AREXS, H., AND EGGERT, J.: "Direct Positive Silver Emulsion," Agfa 
Veroeffentl., III (1934), p. 166. 

ARENS, H.: "New Characteristic Surfaces," Agfa Veroffentl., IV (1935), 
p. l(i. 

EGGERT, J.: "Some Important Light-Sensitive Systems," Phot. J., 76 
(193<i), p. 17. 

2 AREXS, H.: U. S. Patent No. 2,005,837 (1935). 

3 LUMIERE, L., AND SEYEWETZ, W. : Phot. Ind. (1924), pp. 190, 129, 244. 

4 RAHTS, W. : "Use of the Direct Duplicating Film for Miniature Enlarge- 
ments," A? fa Veroeffentl., IV (1935), p. 201. 

DISCUSSION 

MR. GREENE: Is this emulsion adaptable to the methods of reproduction used 
by advertising agencies? 

MR. SCHOECK: It is much too slow for camera work. 

MR. TASKER: Why can it not be used for making motion picture duplicates? 

MR. SCHOECK: Because of its speed, its low sensitivity. The sensitivity is 
below that of contact printing paper. 

MR. TASKER: If we had enough time for making duplicates? 

MR. SCHOECK: Given enough time, it will make direct reproductions. 

MR. TASKER: Of good quality? 

MR. SCHOECK: Well, it is still in the experimental stage. I should say it 
may tend to the hard side. 

MR. MITCHELL: How does the grain size compare with that of ordinary 
duplicating positive stock? 

MR. SCHOECK: About the same as that of direct duplicating emulsion. 



THE BUSINESS SCREEN-SOME DEMANDS MADE BY AND 

UPON IT* 



W. F. KRUSE** 

Summary. Motion pictures have been used for advertising for a number of years, 
but only in the last few years has the use of the business film reached such outstand- 
ing proportions. The majority of such films are now shown on 16-mm. sound 
equipment. 

Some of the applications that have been made and the various groupings into which 
the several types of advertising pictures fall are described, including a brief historical 
explanation of why various types of films came into use. 

The Committee on Non-Theatrical Equipment in its report deals 
in detail with general conditions common to all sections of the non- 
theatrical field. This paper is confined therefore to some specific 
problems confronting the section of the non-theatrical field which, 
for want of a better name, has come to be called the "Business 
Screen." Three questions stand out: 

(1) What is the nature and scope of the "Business Screen"? 

(2) What specific demands does it make upon the motion picture engineer? 
(.?) To what extent have these demands been met? 

THE SCOPE OF THE BUSINESS SCREEN 

A "business film" is, in essence, a sales tool. Its function is to 
tell a sales story to the potential consumer audience. Its sales ap- 
peal may be direct or indirect; it may be timed to tell its story in two 
minutes or two hours; it may have cost $100 to make or $100,000; 
it may be shown on a salesman's projector across a prospect's desk, 
or it may have gala presentations in the finest motion picture theaters 
rented for the occasion. Essentially its purpose is to sell the product 
offered by the film sponsor. 

The universal popularity of the motion picture needs no proof. 
The fact that 80 per cent of the American public's amusement dollar 
goes for motion picture entertainment may be taken as conclusive 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Bell & Howell Company, Chicago, 111. 

431 



432 W. F. KRUSE [j. s. M. P. E. 

evidence. The fact that thousands of progressive school teachers 
look upon the motion picture as a dynamic educator, and regard 
it as the most forceful interest-compeller in their entire arsenal of 
teaching tools, is corroborative. 

For the business man, and particularly for the advertising and sales 
promotion executive, the motion picture quickly demonstrated it- 
self as a unique, powerful medium to catch attention, hold interest, 
carry conviction, and impel favorable action toward the product or 
services presented by means of the film. 

Advertising men are a canny lot. It is their business to know hu- 
man thought-processes and how to influence them. They were 
among the first to recognize how "eye-minded" is the human race. 
From the earliest wood-cut illustrated advertisements, calling for 
the apprehension of runaway slaves, to the luscious, highly colored, 
double-page spreads offering automobiles, refrigerators, bananas, or 
shoe-laces, the advertising man has been far ahead of the Chinese sage 
who is supposed to have uttered the well known bromide that "one 
picture is worth more than 10,000 words." 

No advertising man would be crazy enough to use 10,000 words, 
because nobody would read that many. The smart advertising 
man uses as many pictures and as few words as possible. The 
smartest use movies. 

The advertising man is a keen student of psychology, both experi- 
mental and applied. He knows that a light is the first stimulus that 
can attract and hold the wandering eye of a very young human in- 
fant. If the light (or its embodiment in a brightly colored object) 
is set into motion, the attraction of the human eye toward this stimu- 
lus becomes irresistible. If sound is added, we complete the trinity 
of primary attention-getters light, motion, and sound which en- 
joy a virtual monopoly of sensory approach all through life. 

The talking motion picture combines these three prime movers of 
the human mind in a degree that is not possessed by any other 
medium. The printed page uses the attractive power of light 
through white space and color, and attempts to simulate motion by 
printed speed lines, cartoon sequences, and successive motion pic- 
ture stills the highest compliment, attempted imitation of the 
motion picture. So prevalent has this tendency become that the 
Bell & Howell Company now makes a special "Candid Eye" camera 
to do this job. The radio uses only sound, and its groping in the direc- 
tion of television is in itself a confession of a realization of its primary 



Oct., 1936] THE BUSINESS SCREEN 433 

shortcomings. The talking picture is the only medium that com- 
bines all three primary lodestones of attention light, motion, and 
sound. 

SOME USES AND RESULTS 

The use of the business film has grown to an extent that is hardly 
realized even by the approximately 140 film-producing organizations 
directly catering to the needs of this section of the non-theatrical 
motion picture industry. A recent survey among 3000 business and 
similar agencies reported to be using 16-mm. motion pictures, re- 
vealed the data summarized in Table I. 

TABLE I 
16-Mm. Motion Pictures in 3000 Business and Similar Agencies 

Circulation Firms Length of Picture No. of Pictures 



Free 258 

Controlled 107 

Free and Controlled 41 

Rented and Sold 23 



1-Reel 493 

2-Reels 199 

More than 2 Reels 155 



( 



\ silent 531 

429 ( sound 316 

Films per Firm Firms 

1 253 

2 69 

3 49 

4 20 

5 10 
More than 5 28 



Some results reported by devotees of the "business screen" will 
probably be of interest. A large steamship line reported that 3379 
showings of its films reached 975,000 persons. An automobile 
manufacturer topped this attendance record by showing a baseball 
film to two million persons in a year. 

In some lines specialized coverage means more than mass atten- 
dance. A pharmaceutical house set out to "detail" 107,884 members 
of the medical and allied professions; at the end of a year they had 
reached 105,87398 per cent of the quota. By spending $67,232.93, 
all told, on a film program, they did their job at 62 ! /2^ per head; other- 
than-film methods had previously cost $2.13 per head for the same 
job. 

An anti-freeze manufacturer spent $18,500 for a direct-sales film, 



434 W. F. KRUSE [j. s. M. p. E. 

and sold $600,000 worth of his product at net prices at shows ar- 
ranged by his dealers and jobbers. A motor manufacturer spent 
$5000 for a film, featuring an item selling at only $70 but added 11 
per cent to his profits on that item alone besides the indirect bene- 
fits of general advertising and dealer recognition. 

An oil company spent $25,000 for its first film a 2 -reel comedy on 
sales training. Upon carefully watching reports before and after intro- 
duction of the new advertising medium, they found that sales jumped 
by a general average of 16 per cent following film exploitation. 
Their next program called for $100,000. 

WHAT MAKES A GOOD FILM GOOD? 

To get good results, it takes a good film well made, properly 
shown, and well adapted to its purpose. The question of quality is a 
difficult one to discuss. It is just as hard to say what makes a 
"good" business film as it is to say what makes a good cigar. Too 
many factors enter into the question. The tobacco itself, the blend- 
ing, the workmanship, packing, and merchandising, all play their 
part. But in the last analysis, a lot depends upon the smoker and 
upon "audience." The smoker's own preference and "technic," and 
the extent to which he "harmonizes" with those around him, all con- 
tribute to a composite idea of what makes a "good" or "bad" cigar. 
Similarly with pictures; the product to be presented, the way the 
story is prepared, the showmanship routine worked out to bring 
it to its audience, the effectiveness with which the sponsor's story is 
told in terms that will be favorably received by its audience, all must 
be considered in judging the quality of a film. 

Our survey indicates also that in most business films direct ad- 
vertising is kept at a minimum. There are exceptions, certain films 
made specifically as direct advertising media. A few pictures are as 
direct in their invitation to buy as a department store advertisement 
in a daily newspaper; and a considerable number of pictures, growing 
in importance, are devoted solely to teaching salesmen how to sell. 

There have been business films almost since the birth of the motion 
picture. Some producers boast of more than 20 years of continuous 
production of industrial films. But it is a far cry from the early 
"factory run-arounds" and "good-will" productions to the smart, 
fast-moving, subtly dramatized sales "punch" that goes by the 
name of "business film" today. The modern producer of industrial 
films has a staff comparable to those of theatrical studios in ability, 



Oct., 1936] THE BUSINESS SCREEN 435 

imagination, and often downright genius. His job is really much 
harder: whereas the studio men strive solely to pick an appealing 
story and dish it out in a way they hope the public will like, the indus- 
trial producer must take the other fellow's story of cheese or pig-iron, 
and dress it up in such a way that the public not only will like it, 
but will spend their money, not for the film, but for the product 
plugged by the film. Otherwise, no more pictures and all too 
many firms have had only one picture made. 

CHANGES INTRODUCED BY 16-MM. FILM 

The advent of 16-mm. sound films had far-reaching effects upon 
the business film. Hitherto the film advertiser had been limited 
to the theater, or to portable n on -theatrical set-ups that were generally 
even more cumbersome to arrange. After his film was made, he 
was faced with the problem of dragging audiences into specially pre- 
pared places to see it, or else he resorted to "free-film" circulating 
agencies like the Y. M. C. A., or the U. S. Bureau of Mines, and the 
various State University extension centers. In the theater the 
advertising film was looked upon as an interloper; in the "free" field 
circulation was uncontrolled and was sometimes denounced even by 
some of the very users (teachers) for whom it had been so hopefully 
designed. 

The 16-mm. sound film, like its silent predecessor, made it no longer 
necessary to drag the audience to the film ; instead, the film could go 
out to the audience. With this change an important reorientation 
began to take place as to the content and tone of commercial films, 
and equally so as to their methods of exploitation. The film sponsor 
henceforth could control entirely in his own organization the use to 
which his film production was put, and he was able more accurately 
to check the results attained. He no longer had to camouflage his 
interest in his own film; he could speak of his product as frankly as he 
pleased, provided he did so in a way that would nevertheless keep 
his story interesting to the people to whom he expected to show it. 
Thus, refrigerator manufacturers talk of microbes, automobile 
makers preach safety, loan agencies extol budgets, department stores 
teach care of children and the educational value of toys, lumber 
dealers stress termite protection but all really sell their product in 
terms of customer interest. The film user's own representatives now 
carry their whole show in their own two hands, right into the club, 
school, church, or home where his prospects are gathered. 



436 W. F. KRUSE [J. S. M. P. E. 

SPECIAL FILMS FOR SPECIAL JOBS 

The experienced commercial film user now discriminates as to the 
kind of film to use for certain jobs. Thus a certain motor-car manu- 
facturer carried out a masterpiece "of general advertising in his one- 
reel safety film, Everybody's Business, in which the name of the car 
was hardly mentioned, but in which the product was ever legitimately 
to the fore. The film was run in theaters, schools, police courts, de- 
partment stores, by motor clubs, by the Red Cross, and numberless 
other organizations. This was one of the few advertising films ever 
made of which prints were paid for by outsiders who used the picture 
without the slightest alteration. 

But the same firm uses several other types of films also different 
types to do different jobs. They train their dealers and salesmen with 
direct sales-training films, and some of them are certainly "knock- 
down-and-drag-out" concentrated high-pressure sales dope. And 
they also have thrill films, and newsreels, and even a modernized ver- 
sion of the factory "run-around" but planned for special schoolroom 
use, and for the mechanically inclined buyer; and maybe a bit as de- 
fense mechanism against competitors' factory films, the urge to 
show one's own plant as the "most stupendous and colossal" of all 
time. The well known Hollywood "cycle" disease is infectious also 
among the industrial film users, but more prevalent is the healthier 
demand that each picture be "different" from anything ever done 
before by anybody. 

One other case: a manufacturer of spark-plugs entered the field 
with five different films for as many different jobs : 

(1) A "run-around" to glorify the spark-plug in general, and their own in par- 
ticular. 

(2) A fine entertainment film of racing thrills and spills for the casual club or 
county-fair audience. 

(5) A technical animated film showing the function of the spark-plug and the 
reasons for the particular designs, intended mainly for showing to auto mechanics, 
classes in high school, etc., to the mechanically inclined, and to their dealers as 
technical sales ammunition. 

(4) A newsreel showing a helicopter equipped with their plugs, flying over the 
Maya ruins. This was used when needed to tone down the sales angle. 

(5) A sales training film showing the salesman how to achieve a 100 per cent 
average on new plug sales, dramatized in service-station and garage settings, 
with half a dozen crusty customer skeptics converted (in the film). 

In addition to making their films as "entertaining" as possible, par- 



Oct., 1936] THE BUSINESS SCREEN 437 

ticularly those intended as a sugar-coated approach in a direct con- 
sumer sales drive, many users of industrial films supplement their 
own productions with rented entertainment film, thus rounding out 
the program. 

ENTERTAINMENT AND COOPERATIVE PICTURES 

Most industrialists wish to change their entertainment films fre- 
quently, so they avail themselves of the existing sound-film rental 
library facilities. Others, with long-range programs, buy outright 
such entertainment or educational films of high quality as they regard 
timely and suitable, and, in fact, advertise them as part of their own 
shows. 

Another interesting development is the tendency to make a single 
picture for a group of manufacturers, each of whom has an important 
and non-competitive part in the total product being demonstrated. 

A single film will be used by the motor manufacturer, the tire 
maker, and by purveyors of various incidental parts such as spark- 
plugs, piston rings, roller bearings, gasoline, lubricants, paints, and 
other incidental products. Another variant of this tendency is for a 
manufacturer of an essential part to make a film dealing solely with his 
contribution, this film to be inserted into a larger industrial picture 
already produced, by the vendor of the composite product. 

DEMANDS TO BE MET 

The money spent on the business screen by large manufacturers 
comes back considerably multiplied, in the form of additional profits. 
But this profit is realized only if the exploitation of the film is kept in 
mind at every step of the planning and production. To get any 
good out of a picture program, the film has to be shown to its audience 
just as finely as possible. Audiences today compare the business 
screen presentations with what they have come to be accustomed to in 
the theater. This places a serious problem before the equipment 
manufacturer and the motion picture engineer who designs the equip- 
ment. The average purchasing agent for a film sponsor wants to 
buy a sound projector powerful enough to show brilliant, flickerless, 
evenly illuminated pictures to an audience of 5000 and up, per- 
fectly reproduced sound that can be heard half a mile, self-threading, 
self-operating, self-oiling, fitting into a small brief case, weighing 
perhaps two pounds, and costing maybe ten dollars. 



438 W. F. KRUSE [j. s. M. p. E. 

The motion picture industry has not had these specifications 
very long, but we have all done what we could to meet them. 

A few examples: With a 1000-watt projector 16-mm. film has 
been used in auditoriums seating 3500. Users have reported that a 
750- watt machine is satisfactory for indoor audiences of 1800 and of 
2500, and for outdoor audiences of several thousand. 

It is possible to equalize the screen illumination over the entire 
screen area with a difference of less than 20 per cent between any 
two points chosen anywhere on the screen. It is possible to achieve 
steadiness of the screen image within a tolerance of 1 /300th of the 
linear screen dimension, i. e., a movement of less than x /4 inch on a 
6-ft. projected image. 

It is possible to get 16-mm. sound amplifiers with a 25- watt out- 
put, undistorted within 2 l / 2 per cent. It is possible for the sound 
projector to reproduce a greater frequency range than has thus far 
been printable on 16-mm. film. The present response range (40 to 
10,000 cps.) is adequate for any advertising purpose, and the fact 
that 16-mm. reproducers are used for teaching and demonstrating 
piano and violin is sufficient tribute to their excellence. Improve- 
ments in the laboratory process already perfected will further 
increase the fidelity and range of 16-mm. reproductions. 

Threading and operating has been simplified to such a degree that a 
large battery of machines can be placed in the hands of utterly un- 
trained operators and run satisfactorily with no other guidance than 
the instruction book faithfully used. Furthermore, these same 
machines can be packed by their amateur users, shipped to another, 
and another, similarly untrained operator, and good results repeated. 
Needless to say, such a procedure is not ideal, and the more thor- 
ough the instruction of the operator the better will be the results. 

As to weight, size, and cost, unfortunately thus far these factors 
have remained largely proportionate to the sound and screen lumen 
output. As differentiation proceeded in respect to the work to be 
done by equipment assigned to different types of jobs, so there has 
grown a differentiation in the size, weight, and cost of equipment 
designed to do these various jobs. The present range of available 
models, from auditorium projector to a single suit-case model that 
slips beneath a Pullman berth, indicates that the same differentiation 
of function that governs in the automobile industry will probably 
be paralleled, especially as motion picture projectors more and more 
become articles of mass consumption. 



Oct., 1936 J THE BUSINESS SCREEN 439 

Another demand put to the engineer by the movie-using indus- 
trialist is for a low-cost 16-mm. sound recorder. There have been 
some interesting developments in this field, and the trend is viewed 
with grave misgivings by professional producers of industrial sound 
films. We had a similar situation when the 16-mm. silent camera 
first made its appearance, yet the net result was that hundreds of new 
firms entered the ranks of movie users, and producers turned out 
more films rather than fewer as a result of the "roll your own" film 
movement. 

The motion picture engineer has tried so hard to meet the demands 
of the "business screen" that he may be pardoned if he puts a few de- 
mands of his own to the users of business films. He should .urge the 
abandonment of the idea that it is good business to expect something 
for nothing. He should urge that every commercial use that is made 
of the motion picture be really worthy of the medium. He should 
insist that motion pictures really move, and that talking pictures 
really talk. Productions should be adequate, equipment and ex- 
ploitation programs likewise. He should point out to the uninitiated 
the folly of trying to present a two-hour film to a two-minute audience, 
and, vice-versa, a two-hour story in a two-minute film. He should 
preach tirelessly the gospel that whatever is worth doing at all is 
worth doing well. We are keenly alive to the uses to which our 
products are put, for upon successful and constructive use of our 
product depends the future of our industry. 



NEW MOTION PICTURE APPARATUS 

During the Conventions of the Society, symposiums on new motion picture appara- 
tus are held, in which various manufacturers of equipment describe and demonstrate 
their new products and developments. Some of this equipment is described in the 
following pages; the remainder will be published in subsequent issues of the Journal. 



1000-WATT 16-MM. FILMOSOUND PROJECTOR* 

R. F. MITCHELL AND W. L. HERD** 

The Filmosound 16-mm. sound-film projector is of advanced design, incorporat- 
ing many unusual features, such as a 1000-watt lamp and T-12 bulb, motor drive 
take-up and motor rewind, built-in film humidifier, and many other features. 
It is being used to show 16-mm. sound pictures to audiences up to 4000 persons 
(in the auditorium of the National Geographic Society). This is, perhaps, the 
limit of its capacity; normally it is entirely adequate for an audience of 1000. 
Despite its power, the complete projector, amplifier, loud speaker, cables, and film 
for a complete show, all go into two cases, one weighing about 50 pounds and the 
other about 35, constituting an outfit that is readily portable in an ordinary car. 
The advantage of this for lecturers who must travel from place to place and talk 
to audiences of various sizes is evident. 

Fig. 1 shows the arrangement of the equipment in its two cases. Figs. 2, 3 and 
4 show the essential features of the projectors and amplifier units. The projector 
consists mainly of die-castings. The intermittent movement is similar to that of 
the well known Filmo projector, being of the harmonic cam type and employing 
a single-bladed shutter with an unusually large open segment of 216 degrees. The 
shutter rotates three times for each frame that is projected, thus giving two inter- 
mittent flicks in the picture upon the screen. Due to this design, steady and 
flickerless pictures are readily obtained. The normal screen width recommended 
is about 10 or 12 feet. 

While the projector was being designed, the lamp manufacturers were requested 
to develop a 1000-watt projection lamp using a T-12 bulb. It was realized that 
especially efficient ventilation would be required to permit such a lamp to be used 
satisfactorily. Accordingly, especial attention was given to the fan and ventilat- 
ing system of the projector. The 1000-watt lamp in a T-12 bulb, with the efficient 
ventilation provided, easily gives its rated life of 25 hours. The main advantage 
is that the arrangement permits the use of short coupled optics, thus utilizing the 
maximum amount of light from the lamp. Accordingly, the optical efficiency of 
the projector is quite high. 

As will be seen in the illustrations, the projector is supplied with reel arms large 



* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Bell & Howell Co., Chicago, 111. 



440 



NEW MOTION PICTURE APPARATUS 



441 



enough to accommodate 1600-ft. reels. A 1600-ft. reel of 16-mm. film is equiva- 
lent to a 4000-ft. reel of standard film. One threading of the machine is sufficient 
for a 50-minute show. The machine can also handle reels of smaller capacity, 
available in 1200-, 800-, 400-, and 100-ft. sizes. 

The speed of the projector is controlled by a centrifugal type of vibrating- 
reed electric governor of extremely efficient design. Speed is guaranteed to be 
constant within 2 per cent, with line voltage variation from 100 to 125 volts. 
As a matter of fact, the governor will compensate for variations from 90 to 130 
volts without noticeable change in the pitch of the reproduced sound. The gover- 
nor is adjustable, having two pre-set positions permitting operation at speeds of 




FIG. 1. 1000-watt 16-mm. Filmosound projector, with humidor unit removed 
to show arrangement. 

16 and 24 frames per second. The regulation of the governor is so close that a 
heavy synchronous motor is not necessary, permitting the projector to be used 
interchangeably on 25-, 50-, and 60-cycle a-c. or d-c., which is an especially im- 
portant feature for lecture or road show work. 

An unusual feature is the use of a separate electric motor for the take-up. Be- 
cause of the large variety of reel sizes that can be accommodated, and because of 
the range of speeds at which the projector will operate, it was found that the con- 
ventional types of drive were not sufficiently reliable. Accordingly, a separate 
take-up motor was designed, the speed of which is controlled by a calibrated rheo- 
stat. In conjunction with the take-up a shock-absorbing snubber has been in- 
corporated which effectively prevents film damage due to inaccurate or bent reels, 
and is really simple in operation and works most efficiently. 



442 



NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 



Another unusual feature incorporated in the take-up motor is the provision of 
special windings permitting this motor to run at high speed in the reverse direc- 
tion for power rewinding. A 1600-ft. reel is rewound in less than one minute. 
A fool-proof change-over switch, provided to switch the motor from take-up to 
rewind, is interlocked with the main switch so as to prevent accidentally switching 
on the take-up motor to rewind during projection. The machine must be turned 
off, the lever set for rewind, and then the main switch turned on again. 

In order to reduce the danger of burning out lamps and to assure the most 
satisfactory operation under varying voltages, the lamp is connected in circuit 




FIG. 2. 16-Mm. Filmosound projector: 

(A) Take-up tension adjustment (D) Humidifier 

(B) Hand setting knob (E) Front titling knob 

(C) Gate operating lever (F) Gear chamber 

(G) Motor brush screws 

with a variable rheostat located in the lamp house where it will be effectively 
cooled. A voltmeter shows the voltage across the lamp. When starting, the 
rheostat is turned all the way down, and is then brought up until the voltmeter 
registers correctly. The voltmeter is illuminated by a pilot lamp, the light from 
which is reflected to the voltmeter by a small polished metal stud to the front left 
of the voltmeter. The pilot light is shielded, and the shield can be rotated to 
direct the light to any part of the projector so that the pilot can be lighted during 
projection without annoying the spectators near the machine. 

A unique feature has been incorporated in this machine namely, an auto- 
matic humidifier. Although the cooling system was found entirely adequate to 
maintain correct operating temperature even when the projector was used in a 
warm room and with high voltage, it was felt desirable to incorporate a humidi- 



Oct., 1936] 



NEW MOTION PICTURE APPARATUS 



443 



fier to restore moisture to the film. This problem is more severe with 16-mm. 
projection than with theatrical work because 16-mm. film is made of acetate 
safety stock, which tends to lose and absorb moisture rather readily. The humidi- 
fier consists of a series of plates of absorbent material inserted into the back base 
of the machine. Moist air passes through a channel from the humidifier to a slot 
through which the film travels. This blast of moist air impinging upon the film 
immediately after projection has been found to add appreciably to the life of the 
film. 

Incidentally, discussing film life, it may be of interest to mention that, in con- 
trast to theatrical projection, in which three or four hundred projections represent 




FIG. 3. 16-Mm. Filmosound projector: 



(A) 
(B) 



18 



Motor clutch lever (/) 

Current supply switch ( J) 

Rewind-run lever (K) 

Lamp voltage control (L 

Motor speed adjustment (M 

Manual framer (N 

Humidifying slot (O) 

Snubber (P) 



Rear titling knob 

Condenser 

Projection lens 

Reflector 

Pilot light and switch 

Exciter lamp housing 

Voltmeter 

Sound head cover 



good film life, it is now possible to project 16-mm. film more than 1000 times 
without appreciable deterioration. In fact, some tests have run to 16,000 pro- 
jections. 

For auditorium use, it is usually required that the projector be tilted down from 
the balcony or up from the main floor. Accordingly, tilt knobs have been provided 
at both front and back, which operate legs for tilting the projector upward or 
downward to an angle of about 10 or 15 degrees. The low, stream -line base is 



444 



NEW MOTION PICTURE APPARATUS [J. s. M. p. E. 



important in this connection because it provides the necessary strength and low 
center of gravity that permits the projector to be tilted with perfect safety even 
when using the large 1600-ft. reels. 

Sound System. The projector is arranged to be used with the special amplifier 

shown in Fig. 4. A shielded cable 
carries the impulse from the photo- 
electric cell to the amplifier. Another 
cord carries the power to the projec- 
tion lamp, motor, and exciter lamp, 
which are controlled at the amplifier. 
The line switch on the projector is left 
in the "on" position. When operating 
two projectors, one machine or the 
other is started with one of the two 
switches provided, depending upon 
which machine is being used. 

The amplifier embodies all the 
necessary conveniences as well as 
several not found in ordinary theater- 
type amplifiers, made necessary be- 
cause of the use made of the equipment 
and, more particularly, because of the 
relative inexperience of operators. For 
example, instead of supplying the usual type of voltmeter and instructing the 
operator to set the voltage input to the power transformer to a certain voltage, 
the voltmeter is supplied with a dial that is blank except for a red area within 
which the pointer is to be adjusted. A line switch is provided with several taps so 
that the operator merely turns it until the voltmeter needle falls within the red 
area. The extent of this area is ten volts. 




123456 76 9 10 

FIG. 4. Filmosound amplifier: 

Microphone volume control 
Microphone jack 
Tone control 
Film volume control 
No. 2 projector switch 
Change-over switch 
No. 1 projector switch 
Amplifier meter 
(9) Amplifier line-switch 
(10) Fuse box 



i i 




FIG. 5. Response curve of amplifier, showing range of tone control 

adjustment. 



In addition to the conventional volume control, a separate volume control is 
provided for the microphone. This feature is used extensively for adding com- 
ments to films, and also permits the equipment to be used as a public address 
system. Because the equipment is intended for use in halls of various sizes and 



Oct., 1936] 



NEW MOTION PICTURE APPARATUS 



445 



acoustic properties, an extensive tone control is quite necessary for satisfactory 
operation. With it the operator can adjust the quality of the output to com- 
pensate, at least to some extent, for the variable acoustic properties of the audi- 
toriums and for various characteristics of recordings. 

The amplifier comprises four stages of amplification, terminating in a class AB 
power stage of four 45 tubes in parallel push-pull. The power stage is driven by a 
type 42 tube, employed as a triode and coupled to the output stage through a suit- 
able transformer. The first stage of amplification consists of a 6C6 pentode re- 
sistively coupled to a 6C6 operating as a triode, Resistance coupling is employed 

Size of Auditor lum-Cu. Ft. 

HMO 




Number of Persons 

FIG. 6. Relation between amplifier output and number of spectators for 
sound-picture reproducing systems. 

throughout, with the exception of the input and the output circuits of the power 
stage. Direct current is supplied by a mercury- vapor rectifier. A type 80 recti- 
fier, complete with power supply and filter, is contained within the loud speaker 
case, and this design permits adequate field excitation for the speaker with no 
loss of regulation in the amplifier circuit. Careful design has resulted in a high- 
gain amplifier, which produces a surprisingly realistic output with a minimum 
of hum and distortion. 

Fig. 5 shows the response curve with the tone control in the high and low posi- 
tions, and indicates the range of control. The normal output of the amplifier is in 
excess of 25 watts, with a total harmonic distortion of less than 5 per cent. Mo- 
mentary peaks in excess of 100 watts and without objectionable distortion have 



446 NEW MOTION PICTURE APPARATUS 

been measured. Considerable difficulty was at first experienced in obtaining a 
single speaker of satisfactory size and weight that would stand up in actual 
service. The unit adopted is a Magnavox speaker made especially for the repro- 
ducer and possessing a rating of 25 watts in continuous operation. It is a 12-inch 
electrodynamic unit, mounted rigidly inside the carrying case. The speaker case 
carries the amplifier and connection cords, and is sufficiently large to constitute 
a satisfactory baffle without being cumbersome. 

Care has been taken to provide all cords with non-interchangeable plugs so that 
incorrect connections are impossible, which is very important for all portable 
service. 

The amplifier is of the conventional a-c. type. However, the user very often is 
forced to operate the equipment on direct current, so arrangements have been made 
to operate the projector motor and lamp on d-c., using only a small portable con- 
verter for supplying a-c. to the amplifier. 

For certain semi-permanent installations, it has been found desirable to supply 
more than one speaker. Auxiliary speakers are furnished complete with cases, 
power supply, and impedance-matching transformers. The circuits have been 
so arranged that additional speakers may be connected as required, and no thought 
need be given by the operator to matching impedances. Fig. 6 shows the rela- 
tion between the size of auditorium and the power necessary to furnish adequate 
sound. Although the curve is empirical, it has proved a useful guide in practice. 

DISCUSSION 

CAPTAIN BRADLEY: How accurate is the rehumidifier? 

MR. MITCHELL: We have no data that actually show how effective it is. 
It is largely relative, depending considerably upon the initial condition of the 
film and upon the conditions under which the film is projected. On a dry day it 
is very effective. 

MR. KELLOGG: How was the original recording of this film made? 

MR. MITCHELL: On 35-mm. At least 95 per cent of the commercial pictures 
are made that way, due to the difficulty of getting the highest sound quality 
directly on the 16-mm. negative. The investment hi actors, lights, and so forth is 
so great that it is not very safe to make the original negative anything but 35-mm. 
There is a very decided and definite saving in making the print on 16-mm. The 
principal saving is in size and portability of equipment. We can get good results 
from equipment of this kind with audiences up to 4000 persons, even though that 
is stretching the capacity of the equipment considerably. 

MR. KELLOGG: The sound is re-recorded from the 35-mm.? 

MR. MITCHELL: Optically reduced, directly. 

MR. GREENE : Were the response curves only transmission curves, or with the 
amplifiers? 

MR. HERD : Transmission curves, amplified from the photocells, not including 
the rest. 



KODASCOPE MODEL E* 

A. E. SCHUBERT AND H. C. WELLMAN** 

The Kodascope model E was designed to provide optimal picture quality at a 
price that the average amateur can afford to pay. Heretofore, low-priced projec- 
tors have involved sacrifices as to quality, illumination, steadiness, flicker, defini- 




FIG. 1. Model E Kodascope. 

tion, and mechanical noise. In the new projector it was decided that these funda- 
mental qualities should be retained, but that some of the features that add 
materially to the cost and are not strictly essential might be omitted. 



* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Eastman Kodak Co., Rochester, N. Y. 



447 



448 



NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 



The Kodascope E was the result (Fig. 1). It has neither still nor reverse, but 
mechanically and optically gives the maximum in performance and illumination. 
It is housed completely in aluminum die castings. The mechanism is rugged 
and extremely simple, and is designed to render satisfactory service for hundreds 
of hours. It has ground shafts throughout, and double bearings for all high-speed 




FIG. 2. Drive mechanism. 



shafts to eliminate noise caused by wear. Gears are cut after the blanks are 
mounted upon the shafts, and each is checked for eccentricity of the pitch circle 
(Fig. 2) . The maximum tolerance allowed in this respect is 0.0005 inch. Contact- 
ing points of the cam-operated intermittent claw are of hardened steel and phe- 
nolic composition, which eliminates metallic click from these fast-moving parts 
and minimizes wear. The pull-down claw is hardend at the wearing points, but 
straightness and flexibility are maintained by copper plating before hardening and 
by buffing away the plating only at the points at which wear might occur. A 



Oct., 1936] 



NEW MOTION PICTURE APPARATUS 



449 



three-bladed shutter, each blade of which covers an angle of 56 degrees, provides 
an open period of 192 degrees. Framing is accomplished by shifting the pull- 
down claw in relation to the aperture. After extensive research to test their worth, 
oil-impregnated bearings were adopted throughout, assuring permanent, positive 
lubrication. There are only two places to be oiled by the user of the machine, 
one for the pull-down claw and one for the main helical gear. 

The lamp house and fan unit were designed particularly for high-wattage lamps. 
The very effective cooling provided results in long lamp life and maximum 




FIG. 3. Lens system and gate, showing film path. 

illumination. The optical system was specially computed to provide adequate 
screen brilliance and picture quality, and although rigidly mounted, it is ex- 
tremely accessible for cleaning. The lamp house top snaps into or out of posi- 
tion; the upper lamp baffle is removable; by removing the lamp, the condenser 
unit slips out for cleaning; and the reflector is equally accessible. 

Threading is simple and conventional. The "out" position of the pull-down 
claw is indicated at the upper sprocket (Fig. 3). When any tooth of the sprocket 
is aligned to this mark, the claw is withdrawn from the gate and the film can be 
threaded without obstruction. Fixed film guides of hardened steel at the sprockets 
eliminate the necessity of opening frames or remembering to close them. Chro- 



450 NEW MOTIOM PICTURE APPARATUS 

mium-plated relieved gates and aperture plates guard against wear and protect 
the film from being scratched or otherwise injured. 

Rewinding is motor driven, simplified by a special patented reel spindle. After 
projecting a film, the take-up reel is merely moved into its free position, the 
rewind belt is placed upon the pulley, and the motor switched on. 

The pedestal is of cast iron, to provide stability. The whole mechanism pivots 
upon the top of the base allowing a 30-degree tilt for aligning with the screen. 

The model E will fulfill a wide range of projection requirements. While the 
2-inch //2. 5 objective is standard equipment, the 2-inch //1. 6, the 1-inch //2. 5, 
the 3-inch//2.0, and the 4-inch //2.5 are available if desired. With these lenses, in 
combination with the 400-, 500-, or 750-watt lamps, it is possible to attain a 
maximum screen illumination of 210 lumens, a length of throw of 80 feet, and a 
picture 9 J /2 feet wide. The standard model is fitted for 400-ft. reels only. In 
conclusion, another feature may be mentioned. The base of the model E is made 
to fit down over the handle of the carrying case, which thus acts as a projection 
stand. 



SYMPOSIUM ON THE SLIDE-FILM 

Due to the considerable increase of interest in, and the use of, slide-film projectors 
of all sorts for educational and commercial purposes, a symposium on the subject was 
held at the Chicago Convention of the Society on April 30, 1936. Following are 
three of the papers presented in the symposium, and the joint discussion that fol- 
lowed two of them. 

IMPROVEMENTS IN SLIDE-FILM PROJECTORS* 
MARIE WITHAM** 



In seeking the perfect complement to the motion film, we come to the younger 
but equally efficient slide-film each performing a definite job. There has never 
been a doubt of the instructional value of still pictures, or slides, whether for educa- 
tional or industrial purposes. In recent years the need for visual selling and vis- 
ual instruction has steadily increased and with this demand has come a con- 
stant growth of the acceptance of the slide-film. 

This medium is known by a multiplicity of names still-films, strip-films, 
film-slides, and so on, but they all refer to a short strip of 35-mm. non-inflamma- 
ble motion picture film upon which has been printed in sequence a series of photo- 
graphs, charts, drawings, or titles. Two designations are now quite generally 
used: in the educational field such films are called filmslides (one word) or 
Picturols; and in the industrial field slide-films; the reason for the two designa- 
tions being perhaps that in the educational field they take the place of the glass 
slide, hence film slide, while in the industrial field the difference lies in the minds 
of the users between motion films and slide films. It would be a distinct service 
to the trade if the SMPE would suggest one standard name as a general desig- 
nation for such still films as are here under consideration.! 

Equipment for projecting such films has been on the market for many years. 
The first standard S. V. E. film stereopticon was originally known as the "Arto." 
A few years after its aggressive distribution began, two of the largest optical con- 
cerns introduced similar equipment: first the Spencer Lens in 1925, and about a 
year later, the Bausch & Lomb slide-film projector. These were followed by slide- 
film attachments for use on standard glass slide projectors, which have not proved 
very convenient or satisfactory. However, new models designed to show slide- 
films only have been produced very rapidly during recent years, and it is with 
regard to this trend of advancement that we are especially interested. 

In the development of motion picture equipment we have gone from little il- 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Society for Visual Education, Inc., Chicago, 111. 
f The editorial style adopted is slide-film. 

451 



452 



SYMPOSIUM ON THE SLIDE-FILM 



[J. S. M. P. E. 



lumination to greater illumination, whereas the progress in slide-film projectors 
has been partially the reverse. The 200-watt Picturol projectors were in wide 
use in schools and industries when a demand came from industry for a small unit 
for use by contact salesmen for showing the pictures to very small groups of per- 
sons. The Society for Visual Education immediately developed the first of a 
series of very small 50-watt projectors, which, because of their efficiency and 
low cost, were widely adopted and utilized during all the years of the recent de- 
pression. The first and most interesting of these, perhaps, was the self-enclosed 
S. V. E. Jam Handy Pocket er, which actually slips into a man's pocket. The unit 









%M 






FIG. 1. Model F Picturol projector. 

was original in design and size, and was the pioneer in utilizing the T-8, 50-watt, 
bayonet base projection lamp. This pocket projector served a definite need, and 
undoubtedly aided in establishing the demand for compactness and portability 
in projection equipment of this type. Subsequently, half a dozen other 50-watt 
models were added to the 5. V. E. line, two of which, like the original, are also self- 
enclosed units. 

The addition of sound to the slide-film permitted larger audiences to be served ; 
with a consequent need for greater illumination, which has been generously 
supplied in the two latest models of single-frame film stereopticons the S. V. E. 
Picturol projector model F, a 200-watt unit (Fig. l), and the even newer Picturol 
projector model Q (Fig. 2), a 100-watt unit. As in all standard single-frame film 
stereopticons, the aperture is the same as that used for silent motion pictures. 
The model F presents some interesting details. Since no shutters are necessary 
in film stereopticons and because of its compact construction, the illumination of 



Oct., 1936] SYMPOSIUM ON THE SLIDE-FILM 453 

the model F 200-watt projector compares favorably on the screen with 400- or 500- 
watt 16-mm. motion picture projectors (Fig. l). 

Optical systems used in film stereopticons are very similar to those utilized in 
motion picture projectors with the exception of the aperture plates and the all- 
important heat-absorbing heat-resisting element without which slide-films can 
not be successfully used if the maximum illumination is to be obtained. Double 
aperture plates, which act as pressure plates to hold the film flat during projec- 
tion, assure a sharp image over the entire screen and also tend to dissipate the 
heat. 

The new model F 200-watt equipment is the first manually operated slide-film 
projector having a rear aperture glass releasing mechanism, a patented feature 
used exclusively for a number of years in the S.V.E. automatic projector de- 




FIG. 2. Model Q Picturol projector. 

signed for advertising purposes. The purpose of the releasing feature is to pro- 
tect the emulsion side of the slide-film while it is being moved between the aper- 
ture glasses. The release operates in synchronism with the operating button by 
means of a cam that moves the rear aperture glass back instantly when the 
operating button is turned in either direction. The glass is held in a free position 
until a complete new frame is brought into position, and is then automatically 
returned to the normal projection position. 

The new model Q projector embodies most of the important features of the 
model F, but has been designed to take care of smaller groups and therefore utilizes 
a 100-watt, T-8, bayonet base projection lamp ; and, due to the location of the 
light-source with respect to the optical system, a remarkable amount of illumina- 
tion has been obtained (Fig. 2). 

In particular reference to the educational field, in which there has always been 
a comparison between the glass slide and the j^/w-slide, it has seemed advisable 
to consider a picture projected from an area larger than that of the single-frame 



454 SYMPOSIUM ON THE SLIDE-FILM [j. S. M. p. E. 

35-mm. film. 5. V.E. has therefore developed a new line of double-frame projec- 
tors to meet not only the need for better quality projection in the classrooms, but 
more particularly, the immediate requirements in the amateur field, in which 
the use of double-frame cameras, such as Retina, Leica, Contax, Super-Nettle 
and the more recent Argus Candid Camera is now rather extensive. These new 
S. V.E. combination projectors accommodate both single-frame and double-frame 
slide-films, and also project 2 X 2-inch glass slides, or individual slide-films of 
either size mounted between two pieces of 2 X 2-inch glass. They have been 
designed to provide greater ease of operation, a better distribution of illumination 
over the double-frame area, and to meet the demand for a more popular priced 
equipment than previously available. Some of the special features of these two 
new models are as follows- The model A A double-frame Picturol projector is 




FIG. 3. Model BB Picturol projector. 

equivalent in many ways to the model F previously described, and is also a 200- 
watt unit; while model BB (Fig. 3) is a 100- watt unit comparable to the model 
Q. Both are provided, however, with two masks, one being the standard 
single-frame aperture and the other a double-frame aperture. The masks are 
easily interchangeable, so that the projector is instantly adapted to take either 
the single-frame or the double-frame film (Fig. 3). 

The head of the projector is of a swivel design so that it will show either hori- 
zontal or vertical pictures by merely turning the head of the projector to the ap- 
propriate position, and it is novel in that it may be swivelled either to the left or 
the right as occasion demands. 

The two most important and entirely new features of the equipment are the 
framing and the take-up. A new framing mechanism has been devised that 
permits the double-frame film to be brought into view with a single half-turn 
movement of the operating button. By merely moving a control button, a single- 
frame film is brought into view by a quarter-turn of the operating button. 



Oct., 1936] SYMPOSIUM ON THE SLIDE-FILM 455 

Since the new double-frame films of a given number of frames are twice as long 
as the single-frame films, and due also to the fact that sound slide-film productions 
run to much greater length than silent, need for a take-up has been created, 
and this feature is embodied on the new S. V. E. model A A. It has a threefold 
purpose : It not only acts as a take-up for the film, but rewinds it ready for pro- 
jection, puts it into its own container, and eliminates handling the film except 
at the ends. A new type of film-can makes it possible to attach the empty can to 
the bottom of the film-track, the film-can acting as a take-up for the strip of film. 
It automatically winds the film from the outside to the inside, so that the film is 
ready for rethreading into the top magazine without the necessity of rewinding 
or otherwise handling the film. 

Up to this time the present single-frame slide-films have seemed to meet the 
needs in the sales field adequately, and it is our opinion that the industrial motion 
picture producers will continue to prefer the single-frame as standard for their 
purpose, but that remains to be seen. 

However, a great deal has been said recently in educational circles about the 
desirability of the use of visual equipment in the classroom where such equip- 
ment is as easily available to the teacher as a book or a map. The Picturol 
method provides just that; and this new tri-purpose equipment with a very 
portable sound-on-disk reproducer will, we believe, adequately fulfill the daily 
requirements of the classroom teacher for visual-auditory equipment, accom- 
panied, of course, by the existing single-frame and the resultant libraries of educa- 
tional double-frame slide -films with sound. 



DEVELOPMENTS IN SOUND SLIDE-FILM EQUIPMENT' 

F. FREIMANN** 



Sound slide-films, or talking still pictures, are being used extensively by large 
national merchandisers as a sales and training medium. The programs, produced 
for these organizations on films and disks, are on the subjects of sales and 
service training, and for inspirational meetings, direct consumer solicitations, 
and on special subjects such as announcement of changes of company policies, 
advertising programs, and so forth. 

These programs consist of a series of interesting still pictures illustrating the 
subject matter, manually synchronized with the audible text by the operator, 
who receives his cues for advancing the pictures from a melodious tone super- 
imposed upon the recording. The pictures are changed as frequently as necessary 
to follow the sequence of the continuity. Each picture is arrested long enough to 
illustrate a thought to be absorbed by the audience. 

Although the pictures are stills they express action, change with such frequency, 
and are of such wide variety that interest never lags. The average program of 15 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** Electro- Acoustic Products Company, Ft. Wayne, Indiana. 



456 SYMPOSIUM ON THE SLIDE-FILM [J. S. M. p. E. 

minutes' duration is comprised of not less than 60 excellent pictures. The films 
are of standard 35-mm. size, and the records are 12- or 16-inch disks, providing 
a program of 9 to 15 minutes per side. 

To most engineers, sound slide-film equipment, and perhaps the medium as a 
whole, appears very elementary. It is interesting to note, however, that the very 
simplicity of the medium and the equipment is the foundation of the commercial 
success that has been attained. 

Although some efforts had been made to promote the use of sound slide-films 
since 1931, during the period of its development only a few commercial organiza- 




FIG. 1. "Illustravox Senior." 

tions adopted the medium, and then exclusively for sales training. In 1933 less 
than 500 machines were in the field. The excellent results achieved by those or- 
ganizations using the medium were so conspicuous that, coupled with the aggres- 
sive promotion of the film producers and equipment manufacturers, over 200 of 
the largest national organizations are now operating more than 20,000 equip- 
ments distributed throughout this country and abroad. Some of the reasons for 
the wide and universal acceptance are briefly : 

(1) The effectiveness of the medium. 

(2) The simplicity and low cost of sound slide-film productions. 

(3) The comparatively short time required to produce a complete show. 

(4) The low cost of duplicates, which can be distributed at the cost of a few 
dollars per set. 

(5) The low cost of equipment, making wide distribution possible. This 
equipment is available at prices ranging from approximately $40 to $120. 

(6) The portability of the equipment and the simplicity of operation. 



Oct., 1936] SYMPOSIUM ON THE SLIDE-FILM 457 

The first commercial machines were a rather crude combination of a standard 
slide-film stereopticon stored in two portable cases housing an amplifier, loud 
speaker, electrical pick-up, and SSVa-rpm. motor and turntable. The combina- 
tion weighed close to 80 pounds. Modern equipment is now available for every 
purpose. The machines are designed for small group showings, for daylight 
showings, and for large audiences of up to 200 persons. They weigh from 20 to 
40 pounds. 

The original combination was modified hi various forms to fulfill efficiently 
the four essential requirements of this type of equipment, namely: 

(/) Projection of a uniformly sharp picture with sufficient brilliance for 
showing in a semi-dark room. 




FIG. 2. "Salesmaker," with translucent screen. 

(2) Acceptable quality of sound to provide pleasing reproduction of music 
and voice with good articulation. 

(5) Portability : the equipment to be light and compact enough to be con- 
veniently carried by man or woman, in the form of a neat package. 

(4) Convenience of operation: provide features enabling the operator to 
set up the apparatus quickly, thread the projector, and show a picture 
with sound, with a minimum of effort and time. 

The Illustravox Senior is representative of a machine for sound slide-film pres- 
entations to large audiences (Fig. 1). Its compactness is evident. The case is 
18 inches high, 17 inches long, and 7Va inches wide. The complete unit weighs 
38 pounds. It embodies a 200-watt stereopticon capableof projecting a 10-ft. 
picture of good quality under favorable room conditions. The principal com- 
ponents contained within the case are the projector, the motor and turntable, 
pick-up, amplifier, and loud speaker. 

The projector is mounted upon a cast aluminum door, which is conveniently 
dropped into the operating position. The metal door provides a firm foundation 



458 SYMPOSIUM ON THE SLIDE-FILM [J. S. M. P. E. 

for the projector, which when in the operating position is adequately ventilated 
by being suspended outside the case. The projector is aligned with the screen 
by a tilting mechanism in the base of the projector. The projectors are equipped 
with a high-quality optical system designed for maximum efficiency and uni- 
formity of light and sharpness of picture. Ample ventilation of lamp and condens- 
ing lenses, coupled with an effective heat-ray filter, minimizing the temperature 
at the film, insures safe operation under all conditions of temperature and humid- 
ity. A comparatively large film magazine accommodating a strip of film fifteen 
feet long, a receding aperture plate to free the film when in motion, and a highly 
polished film-track are incorporated to lessen film wear. 

A governor-controlled, 33 l /3-rpm. motor and comparatively heavy turntable 
provide the constant record speed. A crystal pick-up is used on a balanced tone- 
arm because of its light weight and uniform frequency response. It is a high- 




FIG. 3. "Illustravox Junior." 

impedance device, connected directly to the grid of the first amplifier tube through 
a potentiometer. 

A two-stage amplifier incorporating one type 6D6 tube and two type 43 tubes 
delivers a power output of 4 watts to the speaker. A voltage-doubler type of 
rectifier is used in preference to a power-transformer type because of the smaller 
weight and the adaptibility to universal operation. The amplifier complete with 
tubes weighs but 2 l / 2 pounds. 

An 8-inch electrodynamic loud speaker is mounted in a steel rim in the side of 
the case. It is readily detachable for mounting in an identical rim in a separate 
baffle board. For small group showings the loud speaker remains in the carrying 
case. For large audiences it is mounted in a small baffle board carried in the 
record compartment <^f the case, and is placed below the screen in front of the 
audience. 

The over-all frequency response of the complete sound reproducing equipment 
from pick-up through the speaker varies only 8 db. over a frequency range extend- 
ing from 80 to 6000 cps. 

A volume control and switches for the projector and motor are mounted upon 



Oct., 1936] SYMPOSIUM ON THE SLIDE-FILM 459 

the amplifier chassis and are accessible through the tube access door at the rear 
of the machine. The pictures are advanced by the operator by a remote-control 
cable. With all the controls directly in front of the operator, he can be com- 
fortably seated behind the machine. When the unit is assembled in its carrying 
position it contains all accessories, except the screen, necessary for a complete 
show. 

A medium sized machine developed for individual and small group showings, 
and specifically designed for satisfactory projection under daylight conditions, is 
represented in the Illustravox Salesmaker (Fig. 2). This unit contains all the 
component parts and accessories required for a complete show. It is in effect a 
compact, portable little theater. The unit assembled for transportation is 6*/2 
inches wide, 18 inches high, and 19 inches long, and weighs only 28 pounds. It 
can be set up and put into operation in two or three minutes, wherever a power 
outlet is available. 

The center portion of the case incorporates a rubberized silk translucent screen 
and the loud speaker, and performs the functions of a shadowbox. The front side 
of the case, when removed, exposes the screen and loud speaker. This section 
provides storage space for the records. The rear section when dropped down forms 
the foundation for the amplifier chassis and projector. 

The projector is a 100-watt unit mounted upon a substantial aluminum casting 
which when in the operating position elevates the projector, centering it with 
the screen. The projector can also be mounted in a plane parallel to the case for 
projecting a large picture upon a wall screen. Under such conditions the section 
of the case housing the loud speaker is detached from the base, placed in front of 
the wall screen, and the speaker connected to the amplifier by means of a flexible 
cable. 

The amplifier, motor, and pick-up are within the metal chassis. The amplifier 
differs from that of the Senior machine in that only one power tube is used in the 
output stage, providing an output of 2 l /g watts to a 6-inch speaker. The tubes 
are mounted at the end of the chassis for adequate ventilation and accessibility, 
and protected with a metal tube guard. The pick-up and motor are identical to 
those used in the Senior model. A wide-angle lens of ! 1 /2-inch focal length is used 
to project a picture upon the translucent screen, and a 3-inch focal length lens is 
carried as an accessory for projecting a picture upon a larger screen. 

The Illustravox Junior is a very compact, light-weight machine, designed for 
small group showings and for individual sale presentations (Fig. 3). The case 
containing all components and accessories including a small screen is only 13 inches 
high, 15 3 /4 inches long, and 6 x /4 inches wide, and the complete equipment weighs 
but 20 pounds. It is similar in construction to the Senior machine. A 100-watt 
projector is mounted upon a door in one end of the case which drops down into 
operating position. The position of the door is adjustable for elevating the pro- 
jector. The pictures are advanced by means of a remote-control cord extending 
through the rear of the machine. 

The pick-up and turntable are identical to those of the other models. The 
amplifier is also of the same type, and provides an output of 2 1 /j watts to a 5-inch 
speaker, which is mounted in the side of the case. 

All three models described are made for universal operation, working on either 
direct or alternating current, as well as for alternating current only. 



THE DEPARTMENT OF AGRICULTURE'S EXPERIENCE 
IN THE PREPARATION AND USE OF SLIDE-FILMS* 



C. H. HANSON** 



The preparation and distribution of 35-rhm. slide-films was first undertaken by 
the Department of Agriculture in 1926. The demand for these slide-films has 
grown with surprising rapidity. Last year 11,200 positives were sold from the 
Department's negatives. The interesting thing to note in this connection is that 
during the same period the demand for the glass lantern-slides of the same sub- 
jects dropped to such a low level that the Department no longer feels justified in 
preparing lantern-slide sets of its new lectures. 

To increase the availability of its illustrated lectures on slide-films, the Depart- 
ment annually lets a contract to some commercial concern for the production of 
its negatives and the production and distribution of its positives. The low price 
established for these slide-films has undoubtedly been an important factor in 
getting people to use them. The present price of a slide-film having no more than 
48 frames is 50 cents. The lecture notes to accompany the slide-film are supplied 
free. 

Production Problems. The production of high-grade slide-films involves a 
number of technical difficulties not inherent in making glass slides. From a 
practical point of view the big problem of making a slide-film is how to copy a 
series of illustrations of various kinds and sizes in a single film so as to maintain 
uniformly high quality in the reproduction of full-tone photographs and good 
legibility in drawings, charts, and reading matter. The difficulties involved in 
the Department's work are made more complicated by the requirement that the 
negative must be sufficiently uniform in printing density to permit its being run 
in a motion picture printer on one light. 

The ideal condition for best results is, of course, to have all copy of such size 
as to require the same amount of reduction. As we have found it impracticable 
and too expensive under our conditions to do this, we make the most of our situa- 
tion by concentrating our efforts upon the quality and format of the original copy. 
We prefer photographs rich in detail and halftones and having normal contrast. 
Prints that are contrasty or have large areas of highlight are least satisfactory. 
With the exception of prints on which handwork is required, all prints are made 
upon glossy paper and ferrotyped. The prints are dry mounted upon black card- 
board, 9X11 inches in size. 

Size of Copy and Picture Aperture. The writer believes that real progress in 
the improvement of slide-films can not take place until a larger size of picture 
aperture is established as standard. The present standard 35-mm. aperture is 

* Presented at the Spring, 1936, Meeting at Chicago, 111. 
** U. S. Department of Agriculture, Washington, D. C. 

460 



SYMPOSIUM ON THE SLIDE-FILM 461 

too small and it will be only a matter of a relatively short time before a larger 
size will be used. The limitations imposed by the small picture aperture greatly 
increase the difficulties involved in preparing the copy and making the nega- 
tives. 

Reproduction of Detail. The value of many of the slide-films prepared by the 
Department of Agriculture depends largely upon the satisfactory reproduction of 
detail in the original photographs. A little thought will make it clear that an ex- 
cessive degree of reduction of fine detail in the original will compress the details 
to such an extent as to exceed the resolving power of the emulsion of the film. 
Therefore, under present conditions it is especially desirable to avoid the use of 
large prints when the reproduction of fine detail is important. When the subject 
permits, it is well to trim down large prints and thus obtain better detail. Trim- 
ming is also highly useful in eliminating nonessentials and thus giving emphasis 
to the real subject of interest. 

When trimming prints, when it is possible to do so, it is always advantageous to 
trim to the same format as that of the picture aperture. The advantages are that 
it affords the maximum size of negative image and, in addition, a more pleasing 
screen image because the photograph extends to the edge of the frame. 

Legibility: Its Importance and How to Obtain It. All the Department's slide- 
films contain more or less reading matter, and many contain charts and drawings; 
it is this type of material that gives us our most serious problems. The work is 
done on the assumption that if the screen image is not easily legible it is of little 
educational value. For this reason we constantly strive to get our cooperators to 
simplify and clarify their drawings, charts, etc., and to get our artists to keep down 
the size of the drawings and make the lines and lettering heavy and bold. 

Legibility of Black-and-White Copy. The problem of preparing black-and-white 
copy that will reproduce well in slide-film form is a very real one, so much so that 
the Bureau of Agricultural Economics has found it necessary to prepare two series 
of charts, one for publication and another for use in slide-films. Thus, we have 
found by experience that copy that is well adapted for publication will often not 
be satisfactory for slide-films. 

In general, we have found that to attain legibility on the screen it is necessary 
to limit the material to about 30 to 35 words, with 50 as the extreme limit. It 
may be of interest also to note that tests indicate that the width of a line of 
printed matter should not exceed 28 or 30 letters and spaces for good legibility. 
More definite information along these lines for the guidance of those preparing 
copy is much needed, and it is to be hoped that some qualified agency will under- 
take such studies. 

Lettering and Printed Matter. The legibility of charts, reading matter, etc., 
naturally depends largely upon the copy, and merits much more study than has 
been given it. It is our opinion that hand-lettering is too slow and expensive, and, 
it should be added, too frequently lacking in legibility. Ordinary typewritten 
material should not be used, except in emergency. A small hand printing press is 
most satisfactory, and the use of type should be encouraged. It is doubtful 
whether there is any other practical process which will afford the legibility, 
variety, and quality at a given cost that can be attained with type. It may be 
interesting to know that the drafting section of the Bureau of Agricultural Eco- 
nomics is now using a hand-press for printing most of the lettering used on their 



462 SYMPOSIUM ON THE SLIDE-FILM [j. s. M. P. E. 

statistical charts. The printing is done upon a fine grade of tissue paper, which is 
treated by a commercial process. The printed matter is cut up and pasted to the 
chart. The advantage of the method is that it practically does away with blocking 
out the negative, etc., in addition to reducing the cost and time required to do the 
lettering. 

Most persons prefer white on black, rather than black on white lettering for 
slide-films. Many of our white on black illustrations have been hand-lettered 
with Chinese white, to which is usually added a little glycerin. When fresh, 
this kind of lettering is quite satisfactory, but unfortunately the Chinese white 
is easily rubbed off. Information is needed on how to overcome such difficulties 
in hand-lettering. 

Printing with white ink upon black paper can be successfully done, but requires 
more than usual care and skill. A simple and satisfactory method suggested by 
J. I. Crabtree has been used with satisfaction. It consists in printing with black 
ink upon a gaslight paper such as Azo, then exposing the paper to light, develop- 
ing, and then removing the ink with gasoline or benzine. 

Shape of Aperture. Another matter that merits attention is the shape of the 
picture aperture. Rounded corners may be all right for motion pictures, but they 
certainly are not suitable for slide-films. The truth of this statement is at once 
apparent when the subject is a narrow vertical photograph placed at one side of 
the frame, as is often done to make use of the remainder of the space for lettering. 
If such copy is made to fill the frame, the outer corners of the photograph are 
rounded and the inner ones are square. This can be overcome by decreasing the 
size of the image, but that is an unsatisfactory solution of the problem. The 
corners of the aperture should be square, or but slightly rounded. 

Negative and Positive Problems. Since the miniature camera came into its own, 
the importance of graininess is quite fully recognized, and considerable research 
work has been done on the problem. But more work should be done with special 
application to slide-film making. Much that has been learned about the production 
of fine-grain miniature negatives applies also to slide-films. However, we must not 
lose sight of the fact that although the typical low-contrast miniature negative 
may be quite suitable when used in a condenser type of enlarger for making a print 
on a rather contrasty grade of paper, yet a similar slide-film negative will very 
likely give poor results when printed upon positive film for projection purposes. 
The uses to which the two kinds of negative are adapted are quite different, and 
it is evident that if each is to serve its purpose most effectively they must differ 
in density and gamma. Here is an opportunity for the research worker to come 
to the aid of the practical worker in this field who needs more definite informa- 
tion upon the kind of negative required for best results and how to attain them. 
In addition, we need information on the type of positive that will give the most 
satisfactory results in a projector using a 50-watt lamp, a 100-watt lamp, etc. 
At present no one seems to know. 

In addition to the problems already discussed, we have those of fog, halation, 
and lack of precise definition. Fog and poor definition are usually the result of 
defective equipment, or carelessness, or both. Two questions are pertinent here: 
(1) what type of lens is best suited to this kind of work, and (2) what is the best 
method of obtaining precision focusing? Upon the subject of halation it may be 
said that, judging from exoerience in making lantern slides, we can not expect to 



Oct., 1936] SYMPOSIUM ON THE SLIDE-FILM 463 

attain the best results until we take to the use of non-halation films, both negative 
and positive. It is also believed that the films now commonly used in the produc- 
tion of slide-film negatives are not the best for the purpose. It would be a great 
help if some practical method could be devised for treating these films so as to 
reduce to a minimum the scratching which under present conditions takes place 
rapidly. Needless to say there is a growing demand for slide-films in color. 
Projection Problems. As previously stated, it is the writer's belief that the 
development of slide-film work has been much retarded because of the size of the 
picture aperture chosen as standard by those who pioneered the work. The choice 
made was a natural one. Nevertheless it was undoubtedly a serious mistake so 
far as results are concerned. Those in the Department of Agriculture who have 
given this matter serious study are convinced, in the light of the disappointing 
results attained with present materials and equipment, that we can not hope 
to achieve the improvement desired until an aperture of larger size is established 
as standard. A larger width of film, such as 70 millimeters, might be the best 
solution, but in view of the fact that the Leica or Contax size (24 X 36 mm.) is 
now a standard miniature camera size the world over, that precision cameras of 
the highest order are now readily available, and that printers and projectors are 
also available, we are rather strongly inclined to believe that the Leica size of 
frame would be the most practical solution of the problem. A third choice 
might be a square picture aperture of the maximum size permissible on 35-mm. 
film, possibly unperf orated. If the aperture were square, there would be no need 
of supplying the projector with a revolving front, which is an indispensable feature 
of any good projector for Leica slide-films. In considering this problem, however, 
the desirability of establishing the 2 X 2-inch glass slide as a substandard size 
should be kept in mind, as its development will be greatly influenced by the market 
supply of projectors adapted to its use. The size of the condenser that will cover 
a slide made on a 2 X 2-inch plate is also well suited for use in projecting 24 X 
36-mm. slide-film frames. 

DISCUSSION 

MR. GREENE: What wattage lamp was used in Mr. Freimann's projector? 

MR. FREIMANN: 200-watt, with the beaded screen. 

MR. CRABTREE: Referring to Mr. Hanson's paper, I realize it must be diffi- 
cult to obtain slide-films of uniform quality from submitted subject matter of 
varying quality. I understand that they are rephotographed or recopied in order 
to level up the contrast in the photographic film. 

An alternate scheme would be to use duplicating positive film for the nega- 
tive film in the copying camera. This film has properties such that by using either 
a yellow or a violet filter over the lens when copying, the contrast of the negative 
can be varied, even though all the images are developed for the same time. 
Those who are doing this kind of work may find this a very useful way of levelling 
up the contrasts without changing the time of development. 

MR. MATTHEWS: Mention was made of scratches encountered in a good many 
of these slide-films after they have been used for some time, and I wonder whether 
varnishing the surfaces would not be worth considering as a means of overcoming 
that objection. 

MR. MACHARG: There are several solutions on the market for that purpose. 



464 SYMPOSIUM ON THE SLIDE-FILM U. S. M. P. E. 

One advantage of the single slide-film is that you do protect it, by reason of the 
fact that the positive is at the center of the film, which is 3 inches long and ! 3 / 4 
inches wide, and you do not handle it. By making a little photopack envelope 
you can protect the single slide-film absolutely without interfering with its use. 
Varnishing is not satisfactory; I have tried it, but it does not work so well. 

MR. GREENE : In the theatrical field we are still a long way from ideal condi- 
tions in handling film. It would seem that thorough attention to the design of 
slide-film projectors and equally thorough attention to handling the film would 
very markedly reduce the trouble due to cracking. If a slide-film is used, say, 
twice a month, that is not excessive, is it? Two hundred showings would mean 
100 months, which gives the film a life of something like eight years. 

Another thing that impressed me in the demonstrations was that in one of the 
slides a pillar in the foreground at the lower right-hand corner of the screen was 
in fairly good detail, while the right-hand background of the picture was practi- 
cally invisible. A duplicate was placed upon the screen with the glass slide a few 
minutes later, and all detail in that part of the picture was visible. If they were 
duplicates, it would seem to show there was a very decided lack of illumination 
from the slide-film projector. There apparently seems to be an attempt by those 
who use them to try to use them in fields for which their limited beam power 
makes them unsuitable. 

Another thing: Would it not be possible or feasible to design the slide-film 
projectors so that with the same mechanism the lenses might be interchangeable, 
and so that the high-grade, high-quality photographic lens in the camera might 
be inserted into the bayonet mount on the front of the projector; or would the 
heat of the beam prove detrimental to the lenses? 

MR. COOK : The lenses can be cemented in such a way that the heat from the 
projector will not damage them in any way. 

MR. FREIMANN : It might be remembered that sound slide-films are necessarily 
restricted to equipment, the price of which is a very definite consideration, and 
very seldom is the camera available with every sound slide-film or stereopticon 
projector. The lenses that are now used are the most practical, commercially, 
from the price and quality standpoint. You probably have observed that the 
pictures were quite effective with a 200-watt projector, and after all, the medium 
is intended for showings to comparatively small groups, and should not be com- 
pared to theatrical showings to audiences in excess of 500 persons. 

MR. WOLF: Can someone tell us the extent to which the slide-film is being 
used in industry and in the schools. 

MR. FREIMANN: I am not thoroughly familiar with the amount of film used 
in the educational field. However, the average commercial slide-film is from seven 
to fifteen feet long. Some of the motor companies are releasing programs twice a 
month, having circulations as great as 5000 to 7000 copies. That will furnish 
some idea of the extent to which the medium is used and the amount of film 
consumed. 

MR. GREENE: As regards the high-grade lenses, a bayonet mount for the front 
of the projector could be made more cheaply than the lens could be made, and 
the great number who have their own miniature cameras could then purchase the 
projectors ready for use at a much lower price than if the product were already 
equipped with a lens. 



Oct., 1936] SYMPOSIUM ON THE SLIDE-FILM 465 

MR. CRABTREE: Mr. Hanson, what is the maximum screen size that you 
recommend, and what is the maximum size of audience that usually views them 
with any degree of comfort? There is no question, judging from the samples 
shown, that the quality of the image from the standpoints of brightness and 
definition does not compare with that of the glass slide. 

MR. HANSON: The average size of our audiences is about 50, and for such 
groups we seldom project pictures larger than 5 or 6 feet wide. With regard to 
lack of definition in a few of the Leica-size frames, that is due to the negatives 
being out of focus. Unfortunately, we found it impossible to have the slide-film 
remade before this meeting. 

Nevertheless, I not only agree with Mr. Crabtree that the image of the glass 
slide is superior to that of the slide-film in both quality and brilliance, but confess 
to a personal preference for glass slides in my own work. Public service must, 
however, take precedence over personal preference. It is the duty of our office to 
make our illustrative material available in a form most acceptable and useful to 
our 7000 extension workers located in all the agricultural sections of the country. 
We are giving up glass slides only after having thoroughly tried them out for 25 
years and found them not adapted to the needs of our country agents. As pre- 
viously shown, the demand for our slide-films has grown by leaps and bounds. 
That explains why we are gradually dropping glass slides and giving our attention 
to slide-films. We realize quite fully the deficiencies of the slide-film, and that 
is why I recommend the adoption of a larger size of aperture, which, I am sure, 
will do much to increase materially the efficiency and usefulness of this very 
valuable visual aid. 



COMMITTEES 

of the 
SOCIETY OF MOTION PICTURE ENGINEERS 

(Correct to September 20, 1936; additional appointments may be made at any 
time during the year as necessity or expediency may require) 



L. W. DAVEE 
A. S. DICKINSON 



O. M. GLUNT 
A. G. HARDY 



ADMISSIONS 

T. E. SHEA, Chairman 
M. W. PALMER 
H. RUBIN 

BOARD OF EDITORS 
J. I. CRABTREE, Chairman 



H. GRIFFIN 
D. E. HYNDMAN 



L. A. JONES 

G. E. MATTHEWS 



W. H. CARSON 
O. O. CECCARINI 



COLOR 

J. A. BALL, Chairman 
C. H. DUNNING 
R. M. EVANS 

A. M. GUNDELFINGER 



H. W. MOYSE 
A. WARMISHAM 



H. GRIFFIN 



CONVENTION 
W. C. KUNZMANN, Chairman 

J. H. KURLANDER 



M. W. PALMER 



H. BUSCH 

A. S. DICKINSON 

G. C. EDWARDS 



EXCHANGE PRACTICE 

T. FAULKNER, Chairman 
A. HIATT 
J. S. MACLEOD 



N. F. OAKLEY 
H. RUBIN 
J. H. SPRAY 



T. ARMAT 

G. A. CHAMBERS 



A. N. GOLDSMITH 
A. C. HARDY 



HISTORICAL 

E. THEISEN, Chairman 
W. CLARK 



HONORARY MEMBERSHIP 

J. G. FRAYNE, Chairman 



G. E. MATTHEWS 
T. RAMSAYE 



H. G. TASKER 
W. E. THEISEN 



466 



COMMITTEES OF THE SOCIETY 



467 



E. HUSE 

K. F. MORGAN 



JOURNAL AWARD 

A. C. HARDY, Chairman 



G. F. RACKETT 
E. A. WTLUFORD 



J. CRABTREE 
R. M. EVANS 
E. HUSE 
T. M. INGMAN 



LABORATORY PRACTICE 

D. E. HYNDMAN, Chairman 
M. S. LESHING 
C. L. LOOTENS 
R. F. MITCHELL 



H. W. MOYSE 

J. M. NlCKOLAUS 

W. A. SCHMIDT 
J. H. SPRAY 



MEMBERSHIP AND SUBSCRIPTION 
E. R. GEIB, Chairman 



Atlanta 

C. D. PORTER 

Boston 

T. C. BARROWS 
J. R. CAMERON 
J. S. CIFRE 

Camden & Philadelphia 
H. BLUMBERG 
J. FRANK, JR. 

Chicago 
B. W. DEPUE 
J. H. GOLDBERG 
S. A. LUKES 
R. F. MITCHELL 



Cleveland 
R. E. FARNHAM 
J. T. FLANNAGAN 
V. A. WELMAN 

Hollywood 
J. O. AALBERG 
L. E. CLARK 
G. H. GIBSON 
C. W. HANDLEY 

E. HUSE 

F. E. JAMES 

G. A. MITCHELL 
P. MOLE 

K. F. MORGAN 
G. F. RACKETT 

Minneapolis 
C. L. GREENE 



New York 

G. C. EDWARDS 

J. J. FINN 

G. P. FOUTE 

H. GRIFFIN 

W. W. HENNESSEY 

R. C. HOLSLAG 

M. D. O'BRIEN 

F. H. RICHARDSON 
H. B. SANTEE 
T. E, SHEA 
J. L. SPENCE 
J. H. SPRAY 

Rochester 

E. K. CARVER 

Washington 
N. GLASSER 

F. J. STORTY 



Australia 
H. C. PARISH 

Austria 

P. R. VON SCHROTT 

China 

R. E. O'BOLGE* 



Canada 

F. C. BADGLEY 

C. A. DENTELBECK 

G. E. PATTON 



England 

W. F. GARLING 

R. G. LlNDERMAN 
D. McM ASTER 

R. TERRANEAU 
S. S. A. WATKINS 



468 



COMMITTEES OF THE SOCIETY 



[J. S. M. P. E. 



France 


India 


Russia 


L. J. DlDIEE 


H. S. MEHTA 


A. F. CHORINE 


L. G. EGROT 


L. L. MISTRY 


E. G. JACHONTOW 


F. H. HOTCHKISS 


M. B. PATEL 




J. MARETTE 




Travelling 


Germany 
W. F. BIELICKE 

K. NORDEN 


Japan 
T. NAGASE 
Y. OSAWA 


E. AUGER 
K. BRENKERT 
W. C. KUNZMANN 






D. McRAE 


Hawaii 


New Zealand 


O. F. NEU 


L. LACHAPELLE 


C. BANKS 


H. H. vSTRONG 



MUSEUM 
(Eastern) 

M. E. GILLETTE, Chairman 

T. ARMAT G. E. MATTHEWS T. RAMSAYE 

H. T. COWLING E. I. SPONABLE 

(Western) 

E. THEISEN, Chairman 
O. B. DEPUE J. A. DUBRAY A. REEVES 

NON-THEATRICAL EQUIPMENT 

R. F. MITCHELL, Chairman 

D. P. BEAN E. C. FRITTS J. H. KURLANDER 

F. E. CARLSON H. GRIFFIN E. Ross 

W. B. COOK R. C. HOLSLAG A. SHAPIRO 

H. A. DEVRY A. F. VICTOR 



C. N. BATSEL 
L. N. BUSCH 
A. A. COOK 
L. J. J. DIDIEE 



PAPERS 

G. E. MATTHEWS, Chairman 
M. E. GILLETTE 
E. W. KELLOGG 
R. F. MITCHELL 
W. A. MUELLER 



H. B. SANTEE 
T. E. SHEA 

P. R. VON SCHROTT 

I. D. WRATTEN 



J. I. CRABTREE 
A. S. DICKINSON 
R. EVANS 



PRESERVATION OF FILM 
J. G. BRADLEY, Chairman 
M. E. GILLETTE 
C. L. GREGORY 



T. RAMSAYE 
V. B. SEASE 
W. A. SCHMIDT 



M. ABRIBAT 
L. N. BUSCH 
A. A. COOK 
R. M. CORBIN 
J. A. DUBRAY 



PROGRESS 

J. G. FRAYNE, Chairman 
R. E. FARNHAM 
E. R. GEIB 
G. E. MATTHEWS 
H. MEYER 
V. E. MILLER 



R. F. MITCHELL 
G. F. RACKETT 
P. R. VON SCHROTT 
S. S. A. WATKINS 
I. D. WRATTEN 



Oct., 1936] 



COMMITTEES OF THE SOCIETY 



469 



PROGRESS AWARD 
A. N. GOLDSMITH, Chairman 



M. C. BATSEL 




C. DREHER 


J. I. CRABTREE 




J. G. FRAYNE 




PROJECTION PRACTICE 






H. RUBIN, Chairman 




J. O. BAKER 


J. J. FINN 


R. MIEHLING 


T. C. BARROWS 


E. R. GEIB 


E. R. MORIN 


F. E. CAHILL 


A. N. GOLDSMITH 


M. D. O'BRIEN 


J. R. CAMERON 


H. GRIFFIN 


F. H. RICHARDSON 


G. C. EDWARDS 


J. J. HOPKINS 


J. S. WARD 


J. K. ELDERKIN 


C. F. HORSTMAN 


V. WELMAN 




P. A. McGuiRE 




PROJECTION SCREEN BRIGHTNESS 




C. TUTTLE, Chairman 




A. A. COOK 


W. F. LITTLE 


B. SCHLANGER 


A. C. DOWNES 


O. E. MILLER 


A. T. WILLIAMS 


D. E. HYNDMAN 


G. F. RACKETT 


S. K. WOLF 




H. RUBIN 






PUBLICITY 






W. WHITMORE, Chairman 




J. R. CAMERON 


G. E. MATTHEWS 


P. A. McGuiRE 


J. J. FINN 




F. H. RICHARDSON 




SOUND 






P. H. EVANS, Chairman 




M. C. BATSEL 


K. F. MORGAN 


R. O. STROCK 


L. E. CLARK 


O. SANDVIK 


H. G. TASKER 


F. J. GRIGNON 


E. I. SPONABLE 


S. K. WOLF 




STANDARDS 






E. K. CARVER, Chairman 




F. C. BADGLEY 


R. E. FARNHAM 


N. F. OAKLEY 


M. C. BATSEL 


C. L. FARRAND 


G. F. RACKETT 


L. N. BUSCH 


H. GRIFFIN 


W. B. RAYTON 


W. H. CARSON 


R. C. HUBBARD 


C. N. REIFSTECK 


A. CHORINE 


E. HUSE 


H. RUBIN 


A. COTTET 


C. L. LOOTENS 


O. SANDVIK 


L. DE FEO 


W. A. MACNAIR 


H. B. SANTEE 


A. C. DOWNES 


K. F. MORGAN 


J. L. SPENCE 


J. A. DUBRAY 


T. NAGASE 


A. G. WISE 


P. H. EVANS 




I. D. WRATTEN 




STUDIO LIGHTING 






R. E. FARNHAM, Chairman 




W. C. KUNZMANN 


V. E. MILLER 


E. C. RICHARDSON 


J. H. KURLANDER 


G. F. RACKETT 


F. WALLER 



470 COMMITTEES OF THE SOCIETY 

SECTIONS OF THE SOCIETY 
(Atlantic Coast) 

L. W. DAVEE, Chairman 
H. G. TASKER, Past-Chairman M. C. BATSEL, Manager 

D. E. HYNDMAN, Sec.-Treas. H. GRIFFIN, Manager 

(Mid-West) 

C. H. STONE, Chairman 

R. F. MITCHELL, Past-Chairman O. B. DEPUE, Manager 

S. A. LUKES, Sec.-Treas. B. E. STECHBART, Manager 

(Pacific Coast) 

G. F. RACKETT, Chairman 

E. HUSE, Past- Chairman K. F. MORGAN, Manager 
H. W. MOYSE, Sec.-Treas. C. W. HANDLEY, Manager 



FALL, 1936, CONVENTION 



ROCHESTER, NEW YORK 

SAGAMORE HOTEL 
OCTOBER 12-15, INCLUSIVE 



Officers and Committees in Charge 

PROGRAM AND FACILITIES 

W. C. KUNZMANN, Convention Vice-President 
J. L CRABTREE, Editorial Vice-President 
G. E. MATTHEWS, Chairman, Papers Committee 
H. GRIFFIN, Chairman, Projection Committee 
E. R. GEIB, Chairman, Membership Committee 
W. WHITMORE, Chairman, Publicity Committee 
G. E. MATTHEWS, Chairman, Papers Committee 



G. A. BLAIR 

A. A. COOK 

J. I. CRABTREE 

K. M. CUNNINGHAM 



LOCAL ARRANGEMENTS 

E. P. CURTIS, Chairman 
K. C. D. HICKMAI: 
L. A. JONES 
G. E. MATTHEWS 



I. L. NIXON 
W. B. RAYTON 
E. C. ROLAND 
L. M. TOWNSEND 



E. R. GEIB 



F. E. ALTMAN 
E. K. CARVER 



J. G. CAPSTAFF 
E. K. CARVER 



A. A. COOK 
W. H. REPP 



REGISTRATION AND INFORMATION 

W. C. KUNZMANN, Chairman 

S. HARRIS 

TRANSPORTATION 
C. M. TUTTLE, Chairman 

J. G. JONES J. C. KURZ 

H. B. TUTTLE 

HOTEL ACCOMMODATIONS 

K. M. CUNNINGHAM, Chairman 

A. A. COOK O. SANDVIK 

H. B. TUTTLE 

PROJECTION 

H. GRIFFIN, Chairman 

E. C. ROLAND E. F. TETZLAFF 

L. M. TOWNSEND 



471 



472 FALL CONVENTION [j. s. M. p. E. 

BANQUET 

I. L. NIXON, Chairman 

G. A. BLAIR R. M. EVANS S. E. SHEPPARD 

W. CLARK W. C. KUNZMANN H. B. TUTTLE 

A. A. COOK J. S. WATSON 

PUBLICITY 

W. WHITMORE, Chairman 

F. C. ELLIS J. C. KURZ G. E. MATTHEWS 

E. C. FRITTS W. WESTWATER E. C. ROLAND 

LADIES' RECEPTION COMMITTEE 

MRS. L. A. JONES, Hostess 

assisted by 

MRS. A. A. COOK MRS. C. M. TUTTLB MRS. H. B. TUTTLE 

MRS. R. M. EVANS MRS. S. E. SHEPPARD 

TECHNICAL SESSIONS 

All technical sessions will be held at the Sagamore Hotel (Convention head- 
quarters) except the session on Tuesday morning, which will be held in the audi- 
torium of the Kodak Research Laboratories at Kodak Park. 

HEADQUARTERS 

The Headquarters of the Convention will be the Sagamore Hotel, where 
excellent accommodations are assured. A reception suite will be provided for 
the Ladies' Committee. 

Special hotel rates guaranteed to SMPE delegates, European plan, will 
be as follows: 

One person, room and bath $ 3.50 

Two persons, room and bath 6.00 

Parlor suite and bath, for two 10.00 

Parlor suite and bath, for three 12.00 

Everyone who plans to attend the convention should return his room reserva- 
tion card to the Hotel promptly in order to be assured of satisfactory accommo- 
dations. Registrations will be made in the order in which the cards are received. 
When the Sagamore Hotel is booked to capacity, additional accommodations will 
be provided by the Hotel Arrangements Committee at another hotel in the 
immediate vicinity of the Sagamore. 

A special rate of fifty cents a day has been arranged for SMPE delegates 
who motor to the Convention, at the Ramp Garage, near the Hotel. 

Golfing privileges may be arranged for any of the Convention delegates by 
consulting the Chairman of the Local Arrangements Committee. 

REGISTRATIONS 

Registration Headquarters will be located on the Sagamore Roof. All mem- 
bers and guests are expected to register, as admittance to certain sessions may be 
contingent upon the display of a membership badge or special ticket. Admit' 



Oct., 1936] FALL CONVENTION 473 

tance cards will be issued at the registration desk for the special lecture on Mon- 
day evening and for the invitation luncheons on Tuesday and Wednesday noons 
at Kodak Park and the Bausch & Lomb Optical Company, respectively. Reser- 
vations for the Informal Luncheon on Monday and for the Banquet on Wednes- 
day should be made at the registration desk. 

Identification cards will be honored at Loew's Rochester and the Century and 
Palace Theaters, the latter two through the courtesy of the Monroe Amusement 
Company. 

LADIES PROGRAM 

A tea has been arranged for the ladies at the University Club on Monday after- 
noon, October 12th. On Tuesday there will be a luncheon at one of the country 
clubs, followed by a motor trip around the city. The program for Wednesday is 
being arranged and will be announced later. Thursday will be left open for 
shopping trips and visits to the new Rundel Memorial Library, the Art Gallery, 
and Eastman School of Music. 

ROCHESTER RESTAURANTS 

In addition to the Main Dining Room and the Coffee Shop at the Sagamore 
Hotel, where excellent meals may be obtained, there are several leading restau- 
rants in the downtown district, as follows: 
Laube's Old Spain, 11 East Avenue 
Odenbach's Restaurant, 14 South Avenue 
Odenbach's Coffee Shop, Clinton and Main (Dinner Dancing) 
1078 University Ave. A reasonably priced family restaurant 
Manhattan Restaurant, 25 East Avenue 
Seneca Hotel, 26 Clinton Avenue S. 

INVITATION LUNCHEONS AND INSPECTION TRIPS 

The Eastman Kodak Company has invited all visiting members of the Society 
to a complimentary luncheon at Kodak Park on Tuesday, October 13th at 1:10 
P.M. Inspection trips through the Kodak Park Works and the Kodak Research 
Laboratories will be arranged during the afternoon. 

On Wednesday, the Bausch & Lomb Optical Company has invited all visiting 
members to a complimentary luncheon at their plant on St. Paul Street at 1:10 
P.M. An inspection tour of the plant and the Scientific Bureau will be arranged 
following the luncheon. A special trip through the B & L glass plant will start 
at 8:30 A.M. (at the plant) Wednesday morning. 

The details of several other trips, for which reservations should be made, are as 
follows : 

Stromberg Carlson Telephone Manufacturing Co., 100 Carlson Road. Two- 
hour trip, including engineering and acoustical research laboratories and manu- 
facture and assembly of radio sets and telephone equipment. 

Delco Appliance Corporation, 391 Lyell Ave. Two-hour trip Tuesday and 
Wednesday afternoons. Trip includes examination of finished product display, 
visit to engineering laboratories, and tour of the plant departments housing 
interesting product operations. Registration for visit desired. 

Gleason Works, 1000 University Avenue. One-hour trip showing manufacture 
and assembly of gear machinery. Advance registration desired. 



474 FALL CONVENTION [J . S. M. p. E. 

Taylor Instrument Co., 95 Ames St. Two-hour trip showing manufacture of 
clinical and household thermometers, aneroid barometers, industrial tempera- 
ture recorders and controllers, etc. Engineering and Research Laboratories 
and special display of instruments in operation. Advance registration desired. 

Wards Natural Science Establishment, 302 N. Goodman St. This firm specializes 
in supplying models for museums, schools, and colleges. Trips may be arranged 
at any time without previous registration. 

It is assumed that delegates will arrange for their own transportation for all 
industrial trips with the exception of those to the Bausch & Lomb Optical Co. 
and the Kodak Park Works of the Eastman Kodak Co., for which motor-coach 
service will be provided on the dates specified. 

POINTS OF INTEREST 

The University of Rochester. The University occupies two sites, the original 
location between Prince and Goodman Streets on University Avenue, and the 
River Campus in the southwest section of the city. For nearly seventy years 
after its organization the University was operated as a Liberal Arts College, but 
in 1918 the School of Music was organized through the generosity of the late 
George Eastman, and the school now bears his name. In 1921 it occupied modern 
buildings in the downtown section of the city, including the beautiful Eastman 
Theater. This theater is one of the chief cultural centers of the city, being the 
home of the Rochester Philharmonic Orchestra and the Civic Orchestra, and 
being the scene of many other musical and dramatic events. 

In 1920 the School of Medicine and Dentistry was organized with a generous 
endowment provided largely by Mr. Eastman and the General Education Board. 

The Bausch & Lomb Memorial Laboratory, housing the Department of 
Physics and the Institute of Optics, is located on the River Campus. This 
Institute was organized through the cooperation of Rochester optical industries, 
for the purpose of providing a center of teaching and research in the field of 
optics. 

The total enrollment of all departments of the University exceeds 4000 
students. 

The Genesee River. At the south edge of the city the river connects with the 
New York State Barge Canal. A barge channel is maintained to the center of 
the city at the Court Street dam. Below the dam the river enters a rocky bed 
and passes over five waterfalls having a total drop of 267 feet. These falls 
supply 50,000 horsepower to the city's industries. At the foot of the falls the 
river enters a deep gorge, through which it flows to its mouth on Lake Ontario, 
seven miles north of the business district. A drive north on St. Paul Street 
along the river to Veterans' Memorial Bridge which spans the gorge, and then 
across the bridge and north on Lake Avenue to the lake will be well worth while. 
Two city parks, Maplewood and Seneca, occupy opposite banks of the gorge near 
the Veterans' Bridge. Ontario Beach Park at the north end of Lake Avenue has 
a fine public bathing beach. 

East Avenue. This is one of the finest residential streets in this part of the 
country, extending from the downtown district east and south to Pittsford. 
At 900 East Avenue is located the former home of George Eastman, bequeathed 



Oct., 1936] FALL CONVENTION 475 

by him to the University and now occupied by the President of the University of 
Rochester. 

Colgate-Rochester Divinity School. The campus is situated on a beautiful hill 
adjacent to Highland Park. It consists of a group of fine modern buildings 
grouped around the Divinity Tower, a dominating feature of the landscape. This 
school, organized in 1928 by the Baptist Education Society, combines and con- 
tinues the activities of the Colgate Theological Seminary, formerly of Hamilton, 
N. Y., and the former Rochester Theological Seminary. About 100 students are 
enrolled. 

Durand Eastman Park. This beautiful park extends for two miles along the 
shores of Lake Ontario and extends back through rolling hills covered with trees 
and flowers of many varieties. There is a bathing beach and public golf course. 
The park is reached by driving north on Culver Road to the park entrance. 

Genesee Valley Park. Located along the river adjacent to the River Campus 
of the University. Contains a public golf course, playgrounds, and picnic sites. 

Highland Park. A few minutes drive from the River Campus (east on Elm wood 
to Goodman, north to the park). Contains 3900 varieties of trees, shrubs, and 
perennials. Particularly noted for its display of lilacs, peonies, and azaleas. 

Mendon Ponds Park. A few miles southeast of the city, reached over routes 
15 and 65. The site of an old camping ground of the armies of the expedition 
against the Seneca Indians. Contains three ponds, bridle trails, and picnic 
grounds. 

Powder Mill Park. On the site of an old, carefully hidden powder mill. Con- 
tains a trout fish hatchery, and is a favorite picnic site. Located fifteen miles 
east of the city on route 15. 

Letchworth Park. Located on the upper Genesee River about 50 miles south 
of Rochester. Contains some of the most notable waterfalls and river-gorge 
scenery in the eastern United States. Roads and foot-trails lead to three large 
falls, along the edge of deep rocky gorges and the deep wooded canyon below the 
falls. Picnic sites of unusual beauty abound, and there are cabins for the over- 
night visitor. Take routes 35-253-36-245. 

The Finger Lake Region. This famous scenic region of lakes, hills, and water- 
falls lies within an hour's drive to the south and east of Rochester, and offers 
dozens of motor trips through country of unusual beauty. There are six large 
lakes, the two largest of which, Seneca Lake and Cayuga Lake, are nearly forty 
miles in length. They are surrounded by wooded hills which rise to an altitude of 
2300 feet. There are nine state parks covering an area of 5000 acres and con- 
taining 1000 waterfalls and many scenic gorges. Visitors driving from Rochester 
to Ithaca will pass through the heart of the region. Several routes may be 
chosen passing through points of particular interest. Information and road 
maps for this trip may be obtained at the registration desk, where there will also 
be available maps for those wishing to plan more extended trips. 

Niagara Falls. Ninety miles west of Rochester. May be reached over 
route 104. 



TENTATIVE PROGRAM 



9:00 a. m. 

10:00 a. m. 
to 12:00 p. m. 



12:30 p. m. 



2:00 p. m. 
to 5:00 p. 



MONDAY, OCTOBER 12th 
Registration; Sagamore Hotel Roof. 

Sagamore Roof; Business and General Session. 
Opening Remarks by President H. G. Tasker. (10 Min.) 
Report of the Convention Committee; W. C. Kunzmann, 

Convention Vice-President. (5 Min.) 
Society Business. (20 Min.) 

Election of Officers for 1937. 

Report of the Secretary; J. H. Kurlander. 

Report of the Treasurer; T. E. Shea. 

Report of the Membership Committee; E. R. Geib, Chair- 
man. 
"Slide Rule Sketches of Hollywood;" H. G. Tasker, Universal 

Pictures Corp., Universal City, Calif. (20 Min.) 
"The Development of the Art and Science of Photography in 
the Twentieth Century;" (Illustrated) C. E. K. Mees, East- 
man Kodak Company, Rochester, N. Y. (1 Hour.) 

Main Dining Room ; Informal Luncheon. 

For members and guests. Address of Welcome by the Hon. 
Charles Stanton, Mayor of Rochester; Response by Presi- 
dent Tasker. Speakers: Dr. Howard Hanson, Director, 
Eastman School of Music ; and others whose names will be 
announced later. 



Sagamore Hotel Roof; Sound and Apparatus Session. 
Report of the Sound Committee; P. H. Evans, Chairman. 

(15 Min.) 

"A Record Word-spotting Mechanism;" R. H. Heacock, 
RCA Manufacturing Co., Inc., Camden, N. J. (25 Min.) 
"Modern Loud Speaking Telephones and Their Develop- 
ment;" C. Flannagan, R. Wolf, and W. C. Jones, Elec- 
trical Research Products, Inc., New York, N. Y. (25 Min.) 
"A Review of the Quest for Constant Speed;" E. W. Kellogg, 
RCA Manufacturing Co., Inc., Camden, N. J. (25 Min.) 
Symposium on Projector-Testing Devices. 
"A New Type of Peak Reading Volume Indicator;" F. L. 
Hopper, Electrical Research Products, Inc., New York, 
N. Y. (15 Min.) 

"A Neon Type Volume Indicator;" S. Read, Jr., RCA 
Manufacturing Co., Inc., Camden, N. J. (15 Min.) 



476 



Oct., 1936] FALL CONVENTION 477 

"A Neon Tube Oscilloscope as a Utility Instrument for the 
Projection Room;" F. H. Richardson, Motion Picture 
Herald, New York, N. Y., and T. P. Hover, Ohio Theater, 
Lima, Ohio. (Demonstration) (15 Min.) 
"The Schwarzkopf Method of Identifying Criminals;" J. 
Frank, Jr., International Projector Corp., New York, N. Y. 
(Demonstration.} (20 Min.) 

"Medical Motion Pictures in Color;" H. B. Tuttle, Eastman 
Kodak Co., Rochester, N. Y. (Demonstration.} (20 Min.) 
Demonstration Film Showing Several Applications of Photog- 
raphy with Polarized Light. (Courtesy of American Society 
of Cinematographers, Inc., Hollywood, Calif.} (15 Min.) 

8:15 p. m. Eastman Theater; Special Lecture Demonstration. 

"Color Photography" (with demonstrations and motion 
pictures); C. E. K. Mees, Vice- President and Director of 
Research, Eastman Kodak Company, Rochester, N. Y. 



TUESDAY, OCTOBER 13th 

9:00 a. m. Buses will be at the Sagamore Hotel to transport members and 

guests to the Kodak Research Laboratories at Kodak Park. 

10:00 a. m. 

to 1:00 p. m. Auditorium, Kodak Research Laboratories; General Technical 

Session. 

"The Kodak Research Laboratories;" C. E. K. Mees, East- 
man Kodak Co., Rochester, N. Y. (15 Min.) 
"Manufacture of Motion Picture Film;" E. K. Carver, 

Eastman Kodak Co., Rochester, N. Y. (25 Min.) 
"Stability of Motion Picture Film as Determined by Acceler- 
ated Aging;" J. R. Hill and C. G. Weber, National Bureau 
of Standards, Washington, D. C. (25 Min.) 
"The Care of Slide-films and Motion Picture Film;" C. G. 
Weber and J. R. Hill, National Bureau of Standards, 
Washington, D. C. (25 Min.) 

"Fire Protection in the Motion Picture Industry;" H. Ander- 
son, Paramount Pictures, Inc., New York, N. Y. (25 Min.) 
"The Projection of Lenticular Color-Films;" J. G. Capstan", 
O. E. Miller, and L. S. Wilder, Eastman Kodak Co., Roches- 
ter, N. Y. (Demonstration.) (25 Min.) 

1:10 p. m. Invitation Luncheon at the Kodak Park Plant of the Eastman 

Kodak Company. 

2:00 p. m. 

to 5:00 p. m. Inspection tour of Kodak Park and the Kodak Research 
Laboratories. 



478 FALL CONVENTION [j. s. M. p. E. 

WEDNESDAY, OCTOBER 14th 

9:30 a. m. 
to 12:15 p. m. Sagamore Hotel Roof; Optics and Lighting Session. 

"The Art of Lighting;" G. J. Folsey, Jr., Hollywood, Calif. 
(20 Min.) 

"Effect of Lens Aberrations upon Image Quality;" W. B. 
Rayton, Bausch & Lomb Optical Co., Rochester, N. Y. 
(25 Min.) 

"Mercury Arcs of Increased Brightness and Efficiency;" 
L. J. Buttolph, General Electric Vapor Lamp Co., Hoboken, 
N. J. (Demonstration.) (25 Min.) 

Report of the Studio Lighting Committee; R. E. Farnham, 
Chairman. (15 Min.) 

"Recent Developments of High-Intensity Arc Spotlamps for 
Motion Picture Production;" E. C. Richardson, Mole- 
Richardson, Inc., Hollywood, Calif. (15 Min.) 

"Trick and Process Cinematography;" J. A. Norling, Loucks 
& Norling Studios, New York, N. Y. (Demonstration.) 
(20 Min.) 

"A Third-Dimensional Effect in Animated Cartoons;" J. E. 
Burks, Fleischer Studios, New York, N. Y. (Demonstra- 
tion.'} (15 Min.) 

1:10 p. m. Invitation Luncheon at Bausch & Lomb Optical Company. 

Transportation to the Bausch & Lomb Plant will be pro- 
vided. Buses will leave the Sagamore Hotel at 12:30 p. m. 
sharp. 

2:00 p. m. 
to 5:00 p. m. Inspection Tour of Bausch & Lomb and Scientific Bureau. 

7:30 p. m. Oak Hill Country Club; Semi- Annual Banquet. 

Motorcoach transportation will be provided to and from 
the Club by the Transportation Committee. Coaches 
will leave the Sagamore Hotel promptly at 7:00 p. m. 
Presentation of SMPE Journal Award. 
Presentation of SMPE Progress Medal. 
Addresses by Mr. M. H. Aylesworth, Chairman of the Board 
of Directors of RKO Radio Pictures, Inc., and other emi- 
nent members of the industry whose names will be an- 
nounced later. 
Dancing and entertainment. 

THURSDAY, OCTOBER 15th 

9:30 a. m. 

to 12:15 p. m. Sagamore Hotel Roof; Apparatus and Equipment Symposium. 
"A Film-Editing Machine Embodying Optical Intermittent 
Projection;" J. L. Spence, Akeley Camera Co., Inc., 
New York, N. Y. (15 Min.) 



Oct., 1936] FALL CONVENTION 479 

"New Recording Equipment" and "An Improved Reel-end 
Alarm;" D. Canady and V. A. Wellman, Canady Sound 
Appliance Co., Cleveland, Ohio. (25 Min.) 
"Three- Wire Direct-Current Supply for Projector Arcs;" 
C. C. Dash, Hertner Electric Co., Cleveland, Ohio. (15 
Min.) 

"A Demonstration Triode Tube;" F. E. Eldredge and H. F. 
Dart, Westinghouse Lamp Co., Bloomfield, N. J. (Dem- 
onstration.) (15 Min.) 
Report of the Standards Comm ttee; E. K. Carver, Chairman. 

(15 Min.) 

"The Use of Visual Equipment in Elementary and Secondary 
Schools;" C. M. Koon, Office of Education, U. S. Depart- 
ment of the Interior, Washington, D. C. (20 Min.) 

2:00 p.m. 
to 5:00 p. m. Sagamore Hotel Roof; Laboratory Session. 

"The Performance Record of an Automatic Recording Densi- 
tometer;" C. M. Tuttle and M. E. Russell, Eastman Kodak 
Co., Rochester, N. Y. (20 Min.) 

"A Developing Machine for Sensitometric Work;" L. A. 
Jones, M. E. Russell, and H. R. Beacham, Eastman Kodak 
Co., Rochester, N. Y. (Demonstration.) (30 Min.) 
"Some Aspects of Reduction Printing;" G. Friedl, Jr., Elec- 
trical Research Products, Inc., New York, N. Y. (25 Min.) 
"Influence of Sprocket Hole Perforations upon the Develop- 
ment of Adjacent Sound-Track Areas;" J. G. Frayne and 
V. Pagliarulo, Electrical Research Products, Inc., Los 
Angeles, Calif. (25 Min.) 

"Improvements in Lenticulated Film;" E. Gretener, Siemens- 
stadt, Germany. (15 Min.) 

APPARATUS EXHIBIT 

There will be no general apparatus exhibit because of the limited display space 
at the Convention headquarters. The Papers Committee, however, is arranging 
the usual Apparatus Symposium on Thursday morning, and would like to be 
notified of any additional papers for this session. 



ABSTRACTS OF PAPERS FOR THE ROCHESTER CONVENTION 
OCTOBER 12-15, 1936 

The Papers Committee submits the following abstracts of papers for the con- 
sideration of the membership. It is hoped that the publication of these abstracts 
will encourage attendance at the meeting and facilitate better discussion of the 
papers. 

G. E. MATTHEWS, Chairman 

C. N. BATSEL M. E. GILLETTE H. B. SANTEE 

L. N. BUSCH E. W. KELLOGG T. E. SHEA 

A. A. COOK R. F. MITCHELL P. R. VON SCHROTT 

L. J. J. DIDIEE W. A. MUELLER I. D. WRATTEN 

"The Development of the Art and Science of Photography in the Twentieth 
Century;" C. E. K. Mees, Eastman Kodak Co., Rochester, N. Y. 

An account of the developments in practical photography during the past 
thirty-five years and of the progress that has been made in our knowledge of the 
scientific principles of photography. 

"A Record Word-Spotting Mechanism;" R. H. Heacock, RCA Manufacturing 
Co., Inc., Camden, N. J. 

A word-spotting mechanism is described, which replaces the pick-up needle 
upon a predetermined spot of a phonograph record by pressing a remote release 
button after setting three reference readings previously established by the trial 
and error method. 

The pick-up arm is held poised above the record by a direct electromagnetic 
pull upon the back end of the pick-up arm. When this electromagnet is de- 
energized the pick-up falls, due to the pull of gravity. 

The speed of fall may be controlled by means of an adjustable exhaust port 
on an air dashpot. No catches or latches are used to release the arm. A manu- 
ally operated open-circuiting release button is in parallel with a second open- 
circuiting switch in the electromagnet circuit, and this second switch is opened 
each revolution of the turntable by a fixed cam. To release the pick-up, the 
manually operated button is depressed, but the pick-up is not released until the 
second switch is cammed open by the turntable. 

In this way the device is indexed with relation to the radial position of the 
record so that not only may the correct groove be repeatedly selected, but the 
desired portion of the groove may be consistently repeated. The effect of eccen- 
tricity of the record center hole with relation to the recorded grooves is eliminated. 
Variations in the size of the record hole are accommodated by means of a tapered 
centering pin. 

Each of the mechanical parts, with the exception of the cammed turntable 
switch, is rigidly located upon the single pick-up arm unit. All necessary elec- 
trical parts for complete operation of the mechanism on a 105- to 125- volt, 50- 
to 60-cycle supply are located on the underside of the motor board. 

480 



FALL CONVENTION 481 

"Modern Loud Speaking Telephones and Their Development;" C. Flannagan, 
R. Wolf, and W. C. Jones, Electrical Research Products, Inc., New York, N. Y. 

The subject of modern loud speaking telephones is discussed with reference to 
efficiency, power-handling capacity, response-frequency characteristics, and dis- 
tributional characteristics. Improvements and their significance are pointed 
out. The latest types of loud speaker are described and certain development 
problems discussed. 

"A Review of the Quest for Constant Speed;" E. W. Kellogg, RCA Manu- 
facturing Co., Camden, N. J. 

The importance of constant record speed in machines used for reproduction 
of music was realized by Edison and many other pioneers in sound recording. 
Crude performance from other standpoints made it hardly worth while for the 
earlier workers to attempt to obtain extremely high standards of speed con- 
stancy. 

The flyball type of phonograph governor came into the picture and has been 
worked so well that it has not even yet been superseded, although with syn- 
chronous motor drives for certain types of equipment, the governor is no longer 
necessary. 

Recording sound photographically probably began with the work of Alexander 
Graham Bell, who made records upon glass disks; but not until long celluloid 
films were available and the motion picture became thoroughly established, did 
photographic sound recording become a competitor of the disk. As late as 1930 
there were many engineers who advocated the disk for sound picture work. 

While the same general principle applies to both mechanical and photographic 
records, the latter involves certain additional problems. 

Among the earlier workers in this field, the expedients adopted by C. A. Hoxie 
and C. L. Heisler, of the General Electric Company, deserve recognition. Brief 
descriptions and discussions are given of a number of ingenious arrangements 
for improving speed constancy which have been employed by various inventors 
and engineers. Some of these expedients have been applied to record turn- 
tables and some to film equipment. 

"The Schwarzkopf Method of Identifying Criminals;" J. Frank, Jr., Interna- 
tional Projector Corp., New York, N. Y. 

At the present time there are only two means of sight identification generally 
in use the still picture and the police headquarters line-up. Neither is par- 
ticularly effective. The use of a sound motion picture which can be easily 
exhibited to widespread audiences in a short space of time is already regarded as 
one of the most useful developments in this field. Sound-film recording equip- 
ment of both the single- and the double-film type, and for both 16-mm. and 
35-mm. technic, has been developed that provides for a picture about 3 1 / 2 minutes 
long. The special apparatus and the technic developed are described, and actual 
motion pictures of actor-criminals shown to prove the effectiveness of the method. 

"Medical Motion Pictures in Color;" H. B. Tuttle, Eastman Kodak Co., 
Rochester, N. Y. 

Improvements made during the past year in methods, apparatus, and materials 
used in making medical motion pictures, particularly Kodachrome, and the char- 
acteristics of an emulsion suitable for exposure with artificial light are discussed. 
The uses of special accessories for medical motion picture photography are de- 



482 FALL CONVENTION [j. s. M. p. E. 

scribed. A demonstration medical film will be shown at the conclusion of the 
paper. 

"Color Photography;" C. E. K. Mees, Eastman Kodak Co., Rochester, N. Y. 

All processes of color photography depend upon splitting the light into the 
three primary colors red, green, and blue-violet making three separate pictures 
by the three colors, and then combining the three pictures again when they are 
viewed. 

In the earliest processes, three quite separate negatives were made ; from them 
three positives were made; and the latter were projected by means of three 
optical lanterns through suitable color filters so that the images fell on top of 
one another upon the screen and produced a color picture. Then methods were 
invented by which a multitude of tiny color filters covered the whole surface 
of the film, these filters being so small that they are invisible to the unaided eye. 
The picture taken through the filters and then viewed through the filters again 
is thus composed of a multitude of units, each of which is taken and viewed by 
one of the three primary colors. 

A process similar to this is the lenticular film process, in which the film base is 
covered with microscopic lenses which form images of the three filters on the film. 
The three images are then projected again through the three filters fitted to the 
lens of the projector. 

Another method of making the color pictures is to print each of the separation 
negatives, making the prints of colors complementary to the filters through 
which the pictures were taken; and then superimposing the prints so that the 
red filter negative is printed in blue-green ; the green filter negative in magenta ; 
and the blue filter negative in yellow. Essentially, this is the process used in 
producing color reproductions in magazines, each of the separate pictures being 
printed hi its suitably colored ink and the printings being superposed. 

In the multilayer processes, the three separation pictures are made in the 
depth of the film. The film has superimposed layers, each of which is sensitive 
to one of the primary colors. After exposure, the three images are converted 
into dye colors, either by the selective bleaching of dyes present in the coating 
or by the formation of dyes in the layers by coupler development, for instance. 

"Manufacture of Motion Picture Film;" E. K. Carver, Eastman Kodak Co.. 
Rochester, N. Y. 

The manufacture of motion picture film may well be studied from the point of 
view of the research man, the technical man, the manufacturer, the machine de- 
signer, and the personnel man; the efforts of all of whom must be coordinated to 
produce motion picture film successfully. 

The fundamental requirements of manufacturing, after the emulsions and 
support formulas have been worked out, are cleanliness and uniformity. These 
are only to be obtained by a careful elimination of dirt at the source, an elaborate 
system of tests, and meticulous control of all processes. The flow of materials 
should approach as nearly as possible the ideal of continuous production. 

The raw materials used are cotton linters, sulfur, sodium nitrate, camphor, 
and solvents for the nitrate base; cotton linters, acetic anhydride, acetic acid, 
triphenyl phosphate, and solvents for safety base; and hides, silver, nitric acid, 
potassium bromide, and sensitizing dyes for the emulsions. The nitration and 
acetylation of cellulose require more careful control of the original cellulose and 



Oct., 1936] FALL CONVENTION 483 

of the conditions of reaction than is necessary for other purposes, but otherwise 
the standard practice is followed. 

In making the "dope," the cellulose ester, plasticizer, and solvents are carefully 
mixed in large mixers, with continuous filtration. 

The coating or casting is carried out on large drums or wheels many feet in 
diameter and up to approximately five feet in width. With some systems, flex- 
ible metal bands are used in place of wheels. The coating surfaces are carefully 
polished and plated in order to give a smooth surface to the film support. A cur- 
rent of warm air is passed around the periphery of the drum in order to evaporate 
the solvents from the "dope," after which the film support is stripped from the 
wheel and subjected to further treatment, such as subbing, tinting, further drying, 
etc. The subbing is necessary in order to make sure that the gelatin emulsion 
will adhere to the film base. 

The simple processes of emulsion making are well known, and the special de- 
tails can not be discussed in the present paper; but uniformity is here attained, as 
in other parts of the manufacture, by carefully testing all raw materials and rigidly 
controlling all the details of the process, demanding, as well, years of experience on 
the part of the emulsion maker. 

The emulsion coating operation is carried out by passing the film support, 
subbed side down, under a roller partly immersed in a pan of melted emulsion. 
The speed of coating and the temperature of the emulsion govern the thickness of 
the emulsion coating. Immediately after the coating, the emulsion is chilled to 
set it in place, and then dried under carefully controlled humidity, temperature, 
and air-velocity conditions, by passing the film in festoons through a long tunnel 
drier. The air used in drying the emulsion must be controlled as to relative hu- 
midity within a very small range if best results are to be obtained, since the speed 
of emulsions is sensitive to changes in moisture content. 

The slitting and perforating of a film should also be carried out under controlled 
humidity conditions. The slitting is done by revolving knives, equally spaced 
above and below the film, to get a shearing action, the upper knife having a keen 
razor edge, and the lower knife a sharp square edge. The perforating is done by 
punches and dies so accurately made that the punches can not be inserted in the 
dies by hand without injury, although when clamped in the machines, they go 
in and out thousands of times without appreciable wear. Each punch consists 
of eight punching members and eight positioning members. The positioning 
members have tapered ends and fit the holes previously punched so as to position 
the film exactly for the next set of holes to be made. 

The wrapping, storing, and shipping of the film are carefully controlled, and 
every endeavor is made to see that the customer receives the film under the best 
conditions for use. 

"Stability of Motion Picture Films as Determined by Accelerated Aging;" 
J. R. Hill and C. G. Weber, National Bureau of Standards, Washington, D. C. 

Motion picture film of the safety type shows great promise as a material 
upon which to preserve records of permanent value, according to tests made at 
the National Bureau of Standards. This type of film, having a base of cellulose 
acetate, is designed for use where the highly combustible film of the ordinary 
theater type, cellulose nitrate, presents too great a hazard from fire and explosion. 
In addition to its safety features, it appears to have the additional advantage of 



484 FALL CONVENTION [J. S. M. P. E. 

being much more lasting. Both types of film were studied by determining the 
effects of various accelerated aging treatments upon samples of new film. Samples 
of old nitrate were tested also to determine their condition after natural aging. 

The most satisfactory accelerated aging treatment found consists in heating 
the film in a dry oven, at 100 C., a test employed to find the relative stability 
of record papers. The films were tested for physical and chemical properties 
before and after oven-aging tests of various durations, and changes in the proper- 
ties noted. High retention of folding endurance and viscosity, and small increase 
in acidity are considered indicative of stability. The acetate film was found to 
be excellent in these respects. Large losses in folding endurance and viscosity, 
plus large increases in free acid in the material characterized the changes in 
nitrate under the heat test. Its poor stability was further indicated by rapid 
change of resistance to an ordnance test used to determine the condition of 
smokeless powder. 

The cellulose acetate film withstood oven-aging for 120 days without serious 
chemical or physical changes, while the nitrate film deteriorated beyond useful- 
ness after 10 days under the same conditions. The acetate appears to have 
lasting qualities comparable to those of permanent-record papers of high quality, 
and the optimal atmospheric conditions for the preservation of paper records 
are suitable for this film. Nitrate film is perishable, and its deterioration is 
greatly accelerated under warm, moist conditions. The preservation of valuable 
nitrate film is a complicated problem involving both elaborate fire protective 
measures and air-conditioning. 

"Care of Slide-Films and Motion Picture Films in Libraries;" C. G. Weber 
and J. R. Hill, National Bureau of Standards, Washington, D. C. 

Reference libraries of the future may contain files of photographic films in 
addition to shelves of conventional books, if the present trend toward the use 
of films for recording and copying the printed word continues. Hence, it appears 
that librarians, long the custodians of our valuable books and papers, are to be 
confronted with the problems involved in the care of records on photographic 
films. 

The film used for records is of the safety type. It is no more inflammable 
than books; hence it offers no new problems in fire protection. It is very stable 
chemically, and should be lasting if properly made and stored. However, the 
safety film is quite sensitive to moisture changes, and is brittle when dry. It is 
pointed out that satisfactory service requires that the moisture content be con- 
trolled by air-conditioning the storage rooms or vaults. The ordinary type of 
motion picture films have a base of cellulose nitrate which is highly combustible. 
The storage of this type of film presents difficult problems of fire protection, and 
should not be undertaken by anyone not entirely familiar with the problems. 

"Fire Prevention in the Motion Picture Industry;" H. Anderson, Paramount 
Pictures, Inc., New York, N. Y. 

The subject of fire prevention in the Motion Picture industry is extremely 
broad, since the motion picture industry embraces practically every known fire 
prevention problem. 

It is of the utmost importance, because of the combustible nature of motion 
picture film, the necessary consideration that must be given to safety of life in 
the operation of theaters, and the serious financial effect of the interruption of 



Oct., 1936] FALL CONVENTION 485 

studio operations by fire. It is further complicated by the extreme susceptibility 
of sound recording and reproducing equipment and of finished motion picture 
film to fire and water damage. 

Motion picture exchanges under the Motion Picture Producers & Distributors 
of America, Inc., have had an amazingly excellent fire record, the lowest fire loss 
record of any industry in the United States. This is the result of the adoption 
of active fire prevention measures by the exchanges, as described in this paper. 
It is suggested that the Society of Motion Picture Engineers interest itself in ac- 
tive fire prevention work in the industry, and that individual motion picture engi- 
neers keep fire prevention in mind in connection with their work, whether it be 
operation or design. 

In design, where possible, non-combustible materials should be included, and 
the construction should be such that the apparatus is protected as far as possible 
against damage by the water or chemicals used for fighting fire. 

The chemistry of fire extinguishing is discussed, as also the various types of 
fire apparatus. The principal types of fire extinguisher are described, and their 
effectiveness and defects brought out particularly with respect to their application 
to the motion picture industry. A description of experiments made with a new 
type of high-pressure spray system is given. 

The standard methods of fire prevention in laboratory, exchange, and theater 
are discussed, and a detailed description is given of the fire problem in motion 
picture studios. The special apparatus necessary due to the severity of the prob- 
lem, and the organization and procedure of the studio fire department are de- 
scribed. 

While the National Fire Protection Association and insurance companies have 
established standard requirements for the installation of fire equipment in pro- 
jection rooms, exchanges, and in connection with sound equipment, no set of in- 
structions has ever been prepared for the benefit of motion picture projectionists 
at time of fire. The problem constantly arises as how to handle a fire properly in 
the projection room. It is recommended that the SMPE adopt a standard set 
of instructions which will tell the projectionist exactly what to do in case of fire. 

A motion picture showing various fire-preventing devices, and fire apparatus in 
action in a motion picture studio will be shown at the conclusion of the paper. 

"The Projection of Lenticular Color Films;" J. G. Capstaff, O. E. Miller, and 
L. S. Wilder, Eastman Kodak Co., Rochester, N. Y. 

In the projection of lenticular color films a large portion of the incident light is 
lost be absorption in the tricolor filters. To determine the feasibility of satis- 
factorily showing these films in large theaters, an experimental projector was set 
up embodying the few simple changes in standard theater equipment that were 
necessary to obtain the required large increase in screen illumination. 

Successful demonstrations with the apparatus at Loew's Rochester Theater at 
Rochester and the Center Theater at New York have proved that it is quite pos- 
sible to secure enough screen brightness to give a satisfactory showing of the len- 
ticular films in the majority of theaters. 

The principal changes made in the standard projection apparatus in order to 
obtain the greatly increased illumination were as follows: 

(1) Increased Relative Aperture. By substituting an//1.6 projection lens for 
the //2.4 lens commonly used, and by increasing the working relative aperture of 



486 FALL CONVENTION [J. S. M. p. E. 

the 65-ampere high-intensity reflector arc so as to take full advantage of the in- 
creased aperture of the projection lens, it was possible to get 2.25 times the screen 
illumination obtained with the regular equipment. 

(2) Reduction of the Shutter Loss. A further increase was obtained by the 
use of a quicker pull-down and a corresponding reduction in the angle of the 
shutter blades; this may not, however, be feasible in practice. 

(3) Increased Filter Transmission. As a result of numerous practical tests it 
was found to be possible to increase the transmission of the tricolor projection 
niters by 33 per cent, without undue loss of color values. 

(4) Lower Print Density. The excellent tone reproduction obtained in the 
process, together with a modification of the optics of the lenticular film, makes 
possible a substantial lowering of the print density. The resultant increase in 
the brightness of the projected image amounts to some 25 per cent. 

The large increase in the radiant energy directed onto the film has made it 
necessary to employ a heat filter in the condenser system. 

Refinements in the present system are expected to produce additional small 
increases in illumination, and it is believed to be possible to develop other special 
equipment to take adequate care of the few (special) cases where it is necessary to 
project upon an unusually large screen. 

"Effect of Lens Aberrations on Image Quality;" W. B. Rayton, Bausch 
& Lomb Optical Co., Rochester, N. Y. 

Lenses are used to form images for two principal purposes: first, to produce 
the most accurate record possible of the original object; and second, to produce 
a pleasing effect. The character of the image formed by a lens depends upon 
diffraction and upon the residual aberrations left after the designer and the 
manufacturer have done their best. For pictures of the first type it is desirable 
that aberrations be reduced to a minimum, but for pictures of the second type 
they are very often deliberately employed to produce desired effects. In motion 
picture projection, lenses of the first class are doubtless always desired. In 
motion picture photography, some attention has been given to achieving special 
effects by deliberately introducing aberrations into the lens. 

Among the many aberrations that afflict lenses, one of the most important is 
chromatic. Since, in general, only two colors can be brought to a common 
focus, some thought has been given to the question of what two colors are best 
to choose to meet the requirements of various kinds of lighting and different 
types of sensitivity of the emulsion. Recent experiments indicate that for a 
combination of particular interest in motion picture photography, namely, in- 
candescent lighting and super-pan emulsion, no significant difference in perform- 
ance is detectable among lenses of 12-inch focus or less, depending upon whether 
the two colors chosen for chromatism are yellow and violet, or red and violet. 

"Mercury Arcs of Increased Brightness and Efficiency;" L. J. Buttolph, 
General Electric Vapor Lamp Co., Hoboken, N. J. 

The low brightness, 15 candles per square-inch, of the Cooper-Hewitt mercury 
arc, while an asset in industrial illumination, has prevented possible applications 
of the lamp where high brightness and, consequently, small source areas are 
essential for use with reflectors and refractors, and are valuable for use where 
space is at a premium. The Cooper-Hewitt quartz mercury arc represented 
an increase of 500 to 1000 candles per square-inch, which permitted compact 



Oct., 1936] FALL CONVENTION 487 

reflectors but still meant too large a source for satisfactory control by optical 
means. This brightness has still been so low compared with the 10,000 foot- 
candles per square-inch possible with incandescent lamps and the 100,000 charac- 
teristic of the crater of the carbon arc, that little serious thought has been given 
to the mercury arc for projection or for long-range floodlighting work. 

The recent development of so-called super-high-pressure mercury arcs has 
now opened up some of these possibilities. By designing a quartz mercury arc 
to operate at mercury vapor pressures of 20 to 30 atmospheres instead of the 
1 atmosphere characteristic of the older high-pressure arcs, brightness of the 
order of 5000 candles per square-inch is attained in air-cooled lamps. By operat- 
ing water-cooled arcs at higher pressure, brightnesses of 100,000 to 250,000 
candles per square-inch have been attained during rather short lamp lives. Of 
the possibilities ranging in rating from 50 to 10,000 watts, only one unit thus 
far has been standardized for manufacture in the United States. 

The 85-watt, type H-3 mercury lamp may be thought of as a small version of 
the type H-l, 400- watt and the type H-2, 250- watt mercury lamp standardized 
during the past few years. It is operated from a similar reactive transformer 
providing 440 volts for starting and 250 volts at the arc terminals, at a normal 
arc current of 0.4 ampere. It is rated at 35 initial lumens per watt in the arc 
and for a 500-hour life. The quartz tube of the arc proper is enclosed in an 
outer insulating bulb of ordinary glass, which limits the short-wave end of the 
spectrum to about 320 p.m.. Through the visible and near-ultraviolet range the 
spectral distribution is similar to that of other high-pressure mercury arcs except 
for the unusual intensity of the 365 ^m lines. 

The effective dimensions of the light-source or arc proper are about 0.6 by 
0.15 inch, but the discharge is of the constricted type, giving a higher maximal 
brightness than the dimensions would indicate in calculation. 

This arc is of the oxide-coated electrode type, designed only for a-c. operation. 
Since the light output follows approximately the arc current, its intensity is 
variable; and although the flicker is not noticeable directly, it is such as to pro- 
duce stroboscopic effects on moving objects, and may be a limitation in photog- 
raphy or in projection where motion is involved. 

It is believed that the high intensity of the 365 nm lines and the high bright- 
ness of the source may permit application of the lamp to certain of the more 
highly specialized lighting problems in the motion picture industry. 

"Trick and Process Cinematography;" J. A. Norling, Loucks and Norling 
Studios, New York, N. Y. 

Process photography, which is the broad classification given to all branches 
of special and trick cinematography, plays an important part in making today's 
motion picture. Many articles have appeared relating to this subject, but, 
unfortunately, most of them have been devoted only to a discussion of the im- 
portance of this branch of photography and very few writers have divulged any 
of the details of the methods employed. This paper sets forth in general the 
underlying procedure in the various branches of the art, and treats many phases 
thereof in sufficient detail to be fully informative. 

The branches of process photography disclosed include: transitional effects, 
such as dissolves and wipes; matte shots; simple and intricate multiple expo- 
sures; composites and montages; animated titles and presentation effects; 



488 FALL CONVENTION [j. s. M. p. E. 

combined drawing and actual photography; optical trick printers and cameras; 
miniature projection background process; problems in making dupe negatives 
by projection, dodging, etc. Important steps are described and illustrated, and 
special apparatus will be shown and their essential functions and operation 
described. 

"Report of Standards Committee;" E. K. Carver, Chairman. 

Since the last report of the Standards Committee, drawings have been com- 
pleted for a new booklet, changing the form of the drawings to conform to the 
American Standards Association specifications. 

No fundamental changes have been made in the dimensions, but the 16-mm. 
sound-film drawing has been changed to a slight extent to conform better to cur- 
rent practice! 

A sub-committee is at work on the question of a single type of perforation for 
both negative and positive, and the early proposal that a perforation having the 
dimensions of the old negative perforation and the shape of the new positive perf- 
oration be adopted as standard has been brought up again, due to the difficulty 
of accomplishing the adoption of the present standard perforation by the users of 
negative film. 

The proposal made by the German Standards Association that 16-mm. film 
spools be standardized with square holes on each side has been referred to the sub- 
committee on sub-standard film, and a report has been received from them. 

The standardization of 2000-foot reels is still under discussion. 

"The Performance Record of an Automatic Recording Densitometer;" C. M. 
Tuttle and M. E. Russell, Eastman Kodak Co., Rochester, N. Y. 

A recording physical densitometer designed to read strips from the type 116 
sensitometer was described recently in /. Opt. Soc. Amer. This instrument 
has been in service in the sensitometric department of the Kodak Research 
Laboratories for about one year, during which time it has been operated steadily. 
Approximately 100,000 sensitometric strips have been read thus far. The instru- 
ment is capable of an output of about 550 strips per day. 

Experience has shown that more repeatable results are attained with this 
instrument than by routine, visual methods. Comparative data accumulated 
in an experiment lasting several months will be presented, along with a time- 
study of the two methods of densitometry. 

Certain features to be changed in the design of a new instrument will be dis- 
cussed. The new instrument will be improved both as to ruggedness and speed. 

The advisability of using devices of this nature in a release print laboratory 
will depend upon a number of factors, such as initial cost, quantity and quality 
of output, and ease of maintenance. 

"A Developing Machine for Sensitometric Work;" L. A. Jones, M. E. Russell, 
H. R. Beacham, Eastman Kodak Co., Rochester, N. Y. 

The sensitometric testing of photographic materials requires that the testing 
laboratory be able to obtain the same results, with a high degree of precision, for 
identical samples of material, although the individual tests may necessarily be 
made at widely differing times. This necessitates that all the factors tending to 
influence the results be held constant over long periods of time. The present 
communication deals specifically with one particular phase of the sensitometric 
process, namely, the development of the samples. 



Oct., 1936] FALL CONVENTION 489 

The developing machine described is designed particularly for a laboratory in 
which a relatively large volume of sensitometric work must be done. It accom- 
modates sixty strips positioned vertically on six metal racks which can be lowered 
into the developing solution simultaneously, and removed either simultaneously 
or individually, so that different development times may be given conveniently 
to different parts of the load. 

The circulation of the developing solution across the face of the exposed material 
is sufficiently rapid so that further increase in violence of agitation produces little 
if any increase in the rate at which the latent image is converted into metallic 
silver. This circulation is of two general types: A relatively slow but uniform 
movement of the developer in the vertical direction is attained by a motor-driven 
propeller which forces the developer down into a well external to the main tank 
from the lower end of which it spreads out beneath a perforated false bottom in 
the tank and rises throughout the body of the tank, flowing back again into the 
top of the well. Much more violent agitation is accomplished by a set of vertical 
paddles which move back and forth close to the exposed surfaces. Both agitat- 
ing elements are driven by a synchronous motor, thus assuring the same rate of 
circulation at all times. 

The entire developing machine is water -jacketed with thermostatically con- 
trolled constant-temperature water, held at a temperature of 65 == 0.1F. 

A careful analysis of the results obtained with the machine has been made, show- 
ing that the circulation throughout the body of the tank is so nearly uniform that 
the results are not influenced by (a) whether the heavily exposed end of the sensi- 
tometric strip is up or down, (b) the position of the strip within the tank, (c) or 
whether a complete or partial load of strips is developed at one time. Results 
indicate also that the agitation is of sufficient violence that the rate of conversion 
of the latent image into metallic silver is at or near the maximum attainable. 
The uniformity and reproducibility of development attained by using the machine 
are very markedly superior to that attainable with any type of hand- or machine- 
rocked tray with which we have had experience, and the use of this machine marks 
a very definite advance in the precision with which sensitometric values may be 
established. 

"Some Aspects of Reduction Printing;" G. Friedl, Jr., Electrical Research 
Products, Inc., New York, N. Y. 

Information recently obtained by the Standards Committee indicates that vari- 
ous groups of dimensions are used for the picture image on 16-mm. reduction 
prints. These data are set forth and the different conditions are reviewed that 
may exist in the projection of prints reduced from 35-mm. negatives made with 
the present standard camera aperture of 0.631 X 0.868 inch, as well as "old silent" 
films. Some consideration is given also to variables introduced by shrinkage. 

"The Influence of Sprocket-Hole Perforations upon the Development of the 
Adjacent Sound-Track Areas;" J. G. Frayne and V. Pagliarulo, Electrical Re- 
search Products, Inc., Los Angeles, Calif. 

An unmodulated sound-track when developed shows 96-cycle modulation. 
The effect is a maximum at the edge of the sprocket holes and diminishes exponen- 
tially for a distance of approximately 30 mils into the sound-track. A film modu- 
lated with a constant frequency shows 96-cycle amplitude and frequency modula- 
tion over the same area. Both effects are introduced principally during process- 



490 FALL CONVENTION [J. S. M. p. E. 

ing of the film. A film having no sprocket holes on the sound-track side is entirely 
free of these effects. 

APPARATUS PAPERS 

"A New Type of Peak Reading Volume Indicator;" F. L. Hopper, Electrical 
Research Products, Inc., New York, N. Y. 

A new type of volume indicator is described that meets the requirements of 
sound recording. Its advantages are: indication of peak values of voltage ; full 
indication for sounds of short duration; adjustment for slow restoring action for 
greater ease of reading; the device may be given the same sensitivity-frequency 
characteristic as that of the light-valve; use of a well damped long-scale indicat- 
ing type of meter. 

"A Neon Type Volume Indicator;" S. Read, Jr., RCA Manufacturing Co., 
Inc., Camden, N. J. 

A number of gaseous discharge lamps of the neon type have been used to indi- 
cate instantaneous peak amplitudes of audio-frequency voltages. When the 
instantaneous value of the signal voltage increases to the value at which the 
first lamp is adjusted to discharge, the lamp starts to glow. When the voltage 
is still further increased, additional lamps begin to glow as their discharge values 
are reached. As the instantaneous voltage decreases the lamps are extinguished 
in the reverse order. 

Such a device provides a definite indication of the peak value, even though of 
extremely short duration. Due to the persistence of vision, such extremely 
short peaks are not lost, although voltages sustained over longer periods produce 
brighter glows. Only one-half of the voltage wave actuates the neon lamps; 
therefore, either positive or negative peaks may be noted. Any portion of the 
scale may be expanded or compressed as desired. Radiotrons of the Acorn 
type are used so as to achieve a compact unit. 

The device is compared with volume indicators of other types, and some of 
its unique circuits are discussed. Diagrams and performance curves are included. 

"A Neon Tube Oscilloscope as a Utility Instrument for the Projection Room;" 
F. H. Richardson, Motion Picture Herald, New York, N. Y., and T. D. Hover, 
Ohio Theater, Lima, Ohio. 

A neon type of rotating mirror oscilloscope is described intended for routine use 
by projectionists to aid in eliminating noise due to microphonic tubes, improperly 
meshed gears, etc. The parts may be either purchased or built by the projec- 
tionist. 

"Recent Developments of High-Intensity Arc Spotlamps for Use in Motion 
Picture Production;" E. C. Richardson, Mole- Richardson, Inc., Hollywood, 
Calif. 

In order to utilize high-intensity carbon arcs more effectively as sources of 
illumination for photographic purposes, two newly designed high-intensity arc 
spotlamps have been developed. Improvements have been incorporated in the 
design which particularly adapt the lamps for use under modern photographic 
conditions, particularly in the production of colored motion pictures, where uni- 
formity of spectral distribution and intensity are vital factors. 

In the design of the arc mechanism used in these lamps, vital improvements 
are: (1) increased rotational speed of the positive carbon; (2) continuous non- 



Oct., 1936] FALL CONVENTION 491 

intermittent feeding of both positive and negative electrodes; (5) rapid-action 
positive and negative manual adjustments. 

The paper describes in detail the application of "Morinc" flat corrugated 
lenses to the new equipment, and illustrates, by means of graphs, the light dis- 
tribution attained for various beam divergencies. The new equipment has had 
sufficient practical application in motion picture production to have proved its 
worth in photographing under both normal and Technicolor production. 

"Film-Editing Machine Embodying Optical Intermittent Projection;" J. L. 
Spence, Akeley Camera, Inc., New York, N. Y. 

The Akeley-Leventhal editing machine is built around the Leventhal two-stage 
optical compensator, which substitutes an optical intermittent for the usual me- 
chanical intermittent, thereby enabling the film to travel uninterruptedly past 
the projection aperture. 

A single small piece of plate glass rotating once per picture cycle in synchronism 
with the film-feeding sprocket takes the place of the usual intermittent claws or 
intermittent sprocket. The system is a two-stage one, and should not be confused 
with single-stage compensators which make one-half revolution per picture cycle. 

It is possible with this equipment to throw into synchronism a sound-track film 
and a picture film while both films are running. A simple selective means is 
provided for running sound-film only, picture film only, or both together. Reels 
2000 feet long may be run without adjustment. A 6-inch picture having an il- 
lumination of 10 foot-candles is attainable. 

Two motors are used for driving the machine, one constant- and one variable- 
speed. The simple temporary splicer employing the cellophane tape is built into 
the machine. 

"New Recording Equipment;" D. Canady and V. A. Wellman, Canady Sound 
Appliance Co., Cleveland, Ohio. 

A new sound-film recorder for studio or portable use is described. Three 
flywheels in addition to a non-resonant drive sprocket filter enable the machine 
to operate satisfactorily on power lines of poor regulation. Tests have proved 
that violet surges on the power supply line have no noticeable effect upon the 
linear film speed. The recorder is unusually quiet in operation. It can be used 
on the set if need arises. Mention is made of recording lamp improvements, 
and a noise-reduction unit for operation in connection with glow lamps is de- 
scribed. A self-contained semiportable recording amplifier is also discussed. 

"An Improved Reel-End Alarm;" D. Canady and V. A. Wellman, Canady 
Sound Appliance Co., Cleveland, Ohio. 

Scratching and mutilation of release prints by mechanical reel-end alarms in 
projectors are touched upon, and a description of an improved indicating device 
is given. Use is made of a light-source and a photoelectric cell. The light-rays 
from the light-source pass at a tangent to, or across, the film. When the point 
of tangency has been reached, the film that previously obstructed the light-ray 
allows the ray to reach the photoelectric cell, which, in turn, actuates the signalling 
device. The device is positive in action and automatic in operation. Nothing 
mechanical touches the film. 

"Three-Wire D-C. Supply for Projection Arcs;" C. C. Dash, The Hertner 
Electric Co., Cleveland, Ohio. 

The introduction of the non-rotating, high-intensity, low- voltage, d-c. arc has 



492 FALL CONVENTION 

made it desirable to use a d-c. supply of as low voltage as practically possible. 
The auxiliary projection equipment, such as the spotlamp, dissolver lamps, and 
effect machines, are still equipped with arc lamps requiring 55 to 65 volts across 
the arc. In order to obtain the benefits of the new lamps using the Suprex 
type of carbon, it is desirable to have a d-c. source of the proper voltage for each 
type of lamp to be used. 

Two flat-compounded generators may be connected in series so as to have the 
voltage of each generator available or the combined voltage of the two in series. 

There has been developed a double-voltage motor-generator arranged so that 
low voltage is available for the non -rotating high-intensity projection lamps, and 
also double the voltage of the single generator for the auxiliary equipment. 
The design of this type of motor-generator may be such that changing the load 
on either generator does not affect the output voltage of the other generator. 
Performance curves of this two-unit motor-generator set demonstrate the steadi- 
ness of the output voltage with changes of load. 

"A Demonstration Triode for Visualizing Electronic Phenomena;" F. E. 
Eldredge and H. F. Dart, Westinghouse Lamp Co., Bloomfield, N. J. 

To augment theoretical discussion with a practical demonstration, a new type 
WL-787 triode has been developed for visualizing the electronic effect when 
changes are made in the grid and plate voltages of a vacuum tube. 

The filament consists of several parallel oxide-coated wires, all of which are 
located in one plane so that the plate current will be uniformly distributed. 
The anode is the fundamental flat plate mounted parallel to the plane of the 
filament. The grid is a fairly open and conventional structure, mounted between 
the filament and the plate. The side of the anode facing the grid and the fila- 
ment is coated with willemite, which shows a bright greenish fluorescence when 
bombarded by electrons of the plate current. A pronounced and clearly visible 
glow occurs at all points where the electrons strike, resulting in a definite pattern 
of the grid upon the plate. Plate size is such that the action can be observed 
by everyone in a room of reasonable size. Either alternating or direct current 
may be used to heat the filament and to supply the voltages for the grid and 
plate. 

The demonstration triode, therefore, becomes a tool that can be used in the 
classrooms of universities, colleges, and technical schools to supplement the 
theoretical discussions. It is useful also for demonstrating visually any vacuum 
tube phenomena depending upon the fluctuation of the grid voltage to vary the 
plate current. 



JOURNAL 



OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXVII NOVEMBER, 1936 Number 5 

CONTENTS 

Page 
Kinematographic Experiences R. W. PAUL 495 

Use of Motion Pictures in an Accurate System for Timing and 
Judging Horse-Races H. I. DAY 513 

Photographic Race-Timing Equipment 

F. E. TUTTLE AND C. H. GREEN 529 

A New Monitoring Telephone Receiver H. F. OLSON 537 

Use of Silica Gel in Air-Conditioning J. C. PATTERSON 545 

The Pull-Down Movement A. S. NEWMAN 553 

Action Is Needed F. H. RICHARDSON 558 

New Motion Picture Apparatus 

Recent Improvements in the Variable-Width Recording 

System B. KREUZER 562 

A New Rotary Stabilizer Sound Head 

F. J. LOOMIS AND E. W. REYNOLDS 575 

A Sound-Picture Reproducing System for Small Theaters .... 

G. PULLER 582 

A New 16-Mm. Sound-Film Projector C. R. HANNA, 

K. A. OPLINGER, W. O. OSBON, AND S. SENTIPAL 590 
The Magazine Cine-Kodak O. WITTEL 595 

Committees of the Society 600 

Fall Convention at Rochester 

Highlights of the Convention 605 

Papers Program 609 

Society Announcements 613 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors 
J. I. CRABTREE, Chairman 

O. M. GLUNT A. C. HARDY L. A. JONES 

G. E. MATTHEWS 



Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscriptions or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 

Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1936, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is 
not responsible for statements made by authors. 



Officers of the Society 

President: HOMER G. TASKER, Universal City, Calif. 

Past-President: ALFRED N. GOLDSMITH, 444 Madison Ave., New York, N. Y. 
Executive Vice-President: SIDNEY K. WOLF, 250 W. 57th St., New York, N. Y. 
Engineering Vice-President: LOYD A. JONES, Kodak Park, Rochester, N. Y. 
Editorial Vice-President: JOHN I. CRABTREE, Kodak Park, Rochester, N. Y. 
Financial Vice-President: OMER M. GLUNT, 463 West St., New York, N. Y. 
Convention Vice-President: WILLIAM C. KUNZMANN, Box 6087, Cleveland, Ohio. 
Secretary: JOHN H. KURLANDER, 2 Clearfield Ave., Bloomfield, N. J. 
Treasurer: TIMOTHY E. SHEA, 463 West St., New York, N. Y. 

Governors 

MAX C. BATSEL, Front & Market Sts., Camden, N. J. 

LAWRENCE W. DAVEE, 250 W. 57th St., New York, N. Y. 

ARTHUR S. DICKINSON, 28 W. 44th St., New York. N. Y. 

HERBERT GRIFFIN, 90 Gold St., New York, N. Y. 

ARTHUR C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

EMERY HUSE, 6706 Santa Monica Blvd., Hollywood, Calif. 

GERALD F. RACKETT, 823 N. Seward St., Hollywood, Calif. 

CARRINGTON H. STONE, 205 W. Wacker Drive, Chicago, 111. 



See p. 600 for Technical Committees 



KINEMATOGRAPHIC EXPERIENCES 



ROBERT W. PAUL** 

Summary. The first commercial showing of motion pictures in England was 
probably made by two men with six Edison peep-show Kinetoscopes installed in a 
shop in Old Broad Street, London, in 1894. Six duplicates of these devices (which 
had not been patented in England] were built in that year by Paul, and sixty machines 
during 1895. A camera having a cam-driven intermittent movement was also built 
in 1895 from a design by Paul and Acres, the latter an English photographer. Print- 
ing and developing equipment were developed to process the films made with the 
camera. In 1895 a second camera was constructed in which intermittency was 
achieved by means of a modified Geneva stop. The public interest shown in the 
Kinetoscope and its inadaptability for projection stimulated Paul late in 1895 to 
design a projector having an intermittent movement consisting of a seven-toothed star- 
wheel. 

Many interesting experiences in making and exhibiting pictures during 1896 
and subsequent years are described. The first motion picture studio in Great Britain 
was designed and built by Paul in 1899 at Muswell Hill, North London. Trick 
films and scientific pictures were made there as well as other subjects. The project 
was closed about 1910 because it was regarded as too speculative as a side-line to in- 
strument making. 

My first contact with animated photography occurred by chance 
in connection with my business, as a manufacturer of electrical and 
other scientific instruments, which I had started at Hatton Garden, 
London, in 1891. In 1894 I was introduced by my friend, H. W. 
Short, to two men, George Georgiades and George Tragedes, who had 
installed in a shop in Old Broad Street, E. C., six Kinetoscopes, bought 
from Edison's agents in New York. At a charge of twopence per 
person per picture, one looked through a lens at a continuously run- 
ning film and saw an animated photograph lasting about half a min- 
ute. Boxing Cats, A Barber's Shop, and A Shoeblack at Work were 
among the subjects, and the public interest was such that additional 
machines were urgently needed. Finding that no steps had been 
taken to patent the machine, I was able to construct six before the 

* Requested and recommended for publication by the Historical Committee. 
Obtained with the cooperation of E. A. Robins, who was one of the early assistants 
of Mr. Paul. 

** Cambridge Instrument Co., Ltd., London, England. 

495 



496 



R. W. PAUL 



[J. S. M. P. E. 



end of that year. To supply the demand from travelling showmen 
and others, I made about sixty Kinetoscopes in 1895, and, in con- 
junction with business friends, installed fifteen of them at the exhibi- 
tion at Earl's Court, London, showing some of the first of our British 
films, including one of the boat race and derby of 1895. The sight 




FIG. 1. Rotary printer. 

of queues of people, waiting their turn to view them, first caused me 
to consider the possibility of throwing the pictures upon a screen. 
Moreover, it had become evident that the weight of the Kinetoscope 
and the difficulty, at that time, of recharging its accumulators, mili- 
tated against its extensive use. 

Users of my Kinetoscopes shortly after that were refused supplies of 
films by the Edison agents, so I was forced to produce new subjects. 
Film stock, with a matte celluloid base, was procurable from Blair, of 



Nov., 1936] KlNEMATOGRAPHIC EXPERIENCES 497 

St. Mary Cray, Kent. For negatives, Kodak film having a clear base 
was preferred. In Birt Acres I found a photographer willing to take 
up the photography and processing, provided I could supply him with 
the necessary plant, which I did early in 1895. For perforating the 
film I made, for use in an ordinary fly-press, a set of punches, 32 in 
number, made to the Edison gauge and fitted with pilot pins. We 
had no information to guide us in designing a camera, but I worked 
out an idea due to Acres. The film was drawn by a continuously 




FIG. 2. Developing racks and drying drums. 

running sprocket from an upper spool, past the light-opening, or 
gate, to another spool below, and was kept under a slight tension. A 
marginal clamping plate, intermittently actuated by a cam, held the 
film stationary in the gate during each exposure. A shutter, whose 
opening synchronised with the cam, revolved between the lens and 
the gate. In our first trial we failed to get a picture on Black- 
friars Bridge only because we forgot, in our excitement, to attach the 
lens. 

Our printer (Fig. 1) was of the rotary type, consisting merely of a 
sprocket over which the positive and negative films passed together, 
behind a narrow slot illuminated by a gas jet. The sprocket was 
turned by hand at a speed judged by the operator, who inspected the 
negative as it travelled past a beam of red light. For development, a 



498 



R. W. PAUL 



[J. S. M. P. E. 



40-f t. length of film was wound upon a birch frame with spacing pegs. 
Horizontal or vertical troughs held the solutions and washing water. 
At first drying was done in festoons, but a little later on light wooden 
drums (Fig. 2). Our first successful Kinetoscope film was taken in 
February, 1895. We took a fair number of subjects, such as Rough 
SeasatDover,* An Engineer's Smithy, and some comic scenes, in addi- 
tion to the two topical films already mentioned. A number of such 

films, joined as endless bands forty 
feet long, were exported, more es- 
pecially to the United States and to 
Germany, but I do not believe that 
our total output for the year exceeded 
ten thousand feet. 

A POSITIVE INTERMITTENT MOTION 

The intermittent motion in our 
first camera was, as I pointed out 
to Acres, not well suited to give 
accurate spacing, and the pictures 
compared unfavorably in that re- 
spect with the original Edison films. 
So soon as the camera was put into 
use I therefore proceeded to make 
a second, with which many of our 
1895 films were taken. In it I 
adopted a modification of the familiar 
Geneva stop, as used in watches, to 
give an intermittent motion to the 
sprocket. Because the 14-picture 
sprocket of the Kinetoscope had too 
great inertia, I made one of aluminium, one-half the diameter. 

My first projector (Fig. 3) is described in The English Mechanic of 
February 21 and March 6, 1896. It was intended to be sold at a 
price of five pounds, and to be capable of attachment to any existing 
lantern. The seven-toothed star-wheel was driven by a steel finger- 
wheel which acted also as a locking device during the period when 




FIG. 3. Star-wheel intermit- 
tent projector (Feb., 1896). 



* This film was included in the program shown at Koster & Bial's Music Hall, 
New York, on April 23, 1896, when the Armat Vitascope was used to project the 
pictures, 1 



Nov., 1936] 



KlNEMATOGRAPHIC EXPERIENCES 



499 



the shutter was open. The latter was oscillated behind the gate by 
means of an eccentric, and a hand-operated safety shutter was pro- 
vided. Four light spring pads pressed upon the corners of the film, 
which was fed out into a basket. A fault, which I ought to have fore- 
seen, was the unsteadiness caused by the inertia of the spool of films, 
and it became necessary to insert the films, 40 or 80 feet long, singly. 
So this model, by means of which I first saw a motion picture upon 
the screen, was promptly scrapped. 

The next step (Fig. 4) consisted in duplicating the intermittent 




FIG. 4. Second model of intermittent projector (Brit. Pat. No. 4686, 
March 2, 1896). 

sprockets, the film near the gate being kept more or less taut between 
them. 2 At that time the likelihood of shrinkage of the film was not 
realized. The machine had a revolving shutter, in the form of a hori- 
zontal drum cut away on two opposite sides, and a rewind spool was 
provided, driven by a slipping belt. A large handwheel was belted 
to a small pulley upon the fingerwheel spindle, the latter being coupled 
to the shutter spindle by spur gears. After a few of these projectors 
had been put into operation the need for larger spools, to contain a 
series of films, became evident. So additional sprockets were ar- 
ranged to give continuous feed above and below the intermittent 
sprockets. 



500 R. W. PAUL [j. s. M. p. E. 

The projector was furnished complete with lantern and illuminant, 
either arc or limelight. This model was used in all my earlier public 
demonstrations and more than 100 of them were produced, many be- 
ing exported to the Continent and to the United States. One of these 
projectors, used at the Alhambra Theater, is preserved in the Science 
Museum, London, together with a camera (Fig. 5) made in 1896, 
having a precisely similar driving mechanism. Both pi